Performance Benchmark N.8.A.4
Students know how to design and conduct a controlled experiment E/L
Scientific inquiry is defined in the National Science Education Standards (NSES p.23) as “the
diverse ways in which scientists study the natural world and propose explanations based on the
evidence derived from their work. Scientific inquiry also refers to the activities through which
students develop knowledge and understanding of scientific ideas, as well as an understanding of
how scientists study the natural world.” Middle school students should develop their ability to
do inquiry in science classes. As part of inquiry learning, students should be encouraged to ask
questions and design investigations to attempt to answer the questions. However, to be taught to
think and work scientifically, they need to learn how to identify questions that can be studied
scientifically, to design a study so that the most accurate observations can be made, and then to
use evidence from that study to support conclusions. Learning how to design and conduct
controlled experiments is a valuable academic tool to help students develop their inquiry skills.
There are many ways to “do” science. Scientists learn from observing, asking questions, using
models, and by gathering information, data, and evidence from various sources. All of these
methods of science are valuable and students should experience a variety of ways of doing
science. When a scientist wants to test a specific concept or the effect of a specific variable,
using a laboratory or other physical setting, he/she will often design and execute a controlled
experiment. A controlled experiment is one that generally will compare an experimental
sample to a control sample. Both experiments are identical except for one “variable” that is
changed or tested in the experimental sample. For example, if you wanted to see if a plant grew
as well in the dark as it did in the light, you could conduct a controlled experiment that includes
growing plants in the dark, and growing plants in the light. To be sure that the light was the only
thing that affects the outcome, everything else such as temperature, type and amount of soil, and
the amount of water given has to be exactly the same for both groups. Traditionally, students
learn about the “Scientific Method” when being taught about controlled experiments. The
scientific method, although not always used by scientists, is often included as a fundamental
method in textbooks and taught by many teachers as a way to teach about controlled experiments.
Teaching students the scientific method is useful because it helps young minds to learn the
importance of reasoning and developing systematic ways to solve a problem or answer a
question. It also provides a foundation for learning how to conduct a controlled experiment, and
helps students organize and plan a scientific study to answer questions about the natural world.
Students however, must also learn that not all science follows the specific, detailed, step-by-step
process that is called the scientific method. “The scientific method” is not the only scientific
method. Discoveries are made through observations, trial and error, development and use of
models, and various other processes and all of these processes must be encouraged.
For further information related to scientific investigations and inquiry see
MS TIPS Benchmark N.8.A.6.
Students need to be challenged to investigate and analyze questions about nature. This requires
encouraging them to independently develop tests and experiments on their own, rather than
providing them with “cook book” scientific verification labs. They need to learn how to use
evidence to support an answer or an explanation. They need to learn how to record and evaluate
data and results. Through teaching how to design and conduct controlled experiments, students
learn how to identify variables and how to control all the variables in an experiment. Teaching
all of these scientific processes and more can be facilitated by incorporating the scientific method.
We will therefore look at steps generally included in lessons about the scientific method and
controlled experiments. These steps, although not necessarily completed in this specific order,
are: observing, questioning, researching and more observing, hypothesizing, experimenting,
analyzing, communicating, and questioning further. The scientific method can more accurately
be called an “Inquiry Cycle.”
Figure 1. Cyclic nature of scientific investigations.
(From http://www.kerrvilleisd.net/Peterson/HPMS_Science/Documents/Scientific_Method.png)
To read more about how controlled experiments and the scientific method are incorporated into
scientific research, see http://www.societyforscience.org/isef/primer/scientific_method.asp .
Controlled Experiments
A controlled experiment is one that generally will compare an experimental sample to a control
sample. Both experiments are identical except for one “variable” that is changed or tested in the
experimental sample. For example, if you wanted to see if a plant grew as well in the dark as it
did in the light, you would run two tests…one with plants in the dark, and the other with plants
in the light. Everything else such as temperature and the amount of water given has to be exactly
the same for both groups.
Several studies completed by scientists to debunk the idea of abiogenesis provide good examples
of controlled experiments and their benefit of supporting scientific hypothesis and testing
theories. Aristotle believed life came from non life. Beginning in the 1600’s, several studies
ultimately led to the rejection of this theory of spontaneous generation. Francesco Redi used
controlled experiments to disprove spontaneous generation. The figure below illustrates his
controlled experiment. The only difference between the experimental samples was whether or
not flies could directly access the meat. His conclusion was that maggots do not spontaneously
appear out of meat, but rather they come from flies.
Figure 2. Redi’s controlled experiment illustration.
(From http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap1.html)
Other scientists conducted controlled experiments that supported the hypothesis that life only
comes from other life and does not spontaneously appear, Pasteur’s (1800’s) experiments
provided strong evidence that life arose from other life. In this classic experiment, all conditions
were the same for all flasks used, except for the exposure to particles in the air.
Figure 3. Illustration representing Pasteur’s study was retrieved.
(From http://www.microbiologybytes.com/introduction/History.html)
To read more about the scientific studies disproving spontaneous generation see
http://microbiology.suite101.com/article.cfm/spontaneous_generation
These and other experiments were early examples of controlled experiments. They were
repeated many times, and only one variable was altered.
Let’s look now at specific steps used to design and implement a controlled experiment. There
are many resources in text books and on line that discuss the various steps of the scientific
method, which as discussed earlier is not the only method of science, but does serve as a tool
that can be used to teach about controlled experiments.
Designing a Controlled Experiment Requires Identifying a Problem or a Question
By observing the natural world, students can identify questions. In order for a question to be
studied in a controlled experiment, it needs to be something that can be tested scientifically. It
should be specific and limited. It should also be open ended, and not able to be answered with a
simple yes or no.
For further discussion of a Problem visit
http://school.discoveryeducation.com/sciencefaircentral/scifairstudio/handbook/scientificmethod.
html
Hypothesis is Identified Before an Experiment is Designed
Prediction can be used as a hypothesis. Some texts define a hypothesis as an “educated guess”.
While this is partially true, we have to be careful to teach students that it is much more than a
guess. Rather, a hypothesis is a possible answer to the question, and is based on what is known
or understood. A scientific hypothesis should be testable, measurable, specific, and clearly
understood.
To learn more about what a hypothesis is or should be, see
http://www.batesville.k12.in.us/Physics/PhyNet/AboutScience/Hypotheses.html
http://sci.waikato.ac.nz/evolution/Theories.shtml
Experimental results may either support or not support a hypothesis. When results do not
support a hypothesis, the hypothesis should not be called “wrong.” Instead, it can be said that
the hypothesis is not supported based on evidence. When that occurs, the hypothesis could be
reformulated based on observations and another controlled experiment to test the new hypothesis
could be designed. A theory is a hypothesis that is supported after many tests.
Plan a Controlled Experiment
Designing a controlled experiment takes practice and time. The experiment must be replicable,
have sufficient sample sizes, and needs to be designed so that only the variable being tested
varies. A reliable acceptable controlled experiment is sometimes called a “Fair test” which is
one in which only one factor at a time is changed while all other conditions are kept constant.
When designing a controlled experiment, step-by-step procedures should be written, all variables
need to be clearly identified, and a method of gathering data should be developed.
For additional information on fair tests see
http://www.sciencebuddies.org/science-fair-projects/project_experiment_fair_test.shtml
and http://www.sciencebuddies.org/science-fair-projects/project_experimental_procedure.shtml
Many science fair related sites provide explanations and examples of the scientific method and
often times science fair organizers prefer the “traditional” scientific method as a standardized
format for entries.
To learn more about science fair and science fair projects visit
Discovery Education http://school.discoveryeducation.com/sciencefaircentral/
Science Stuff.com at http://sciencefairproject.virtualave.net/scientific_method.htm
Science Buddies at http://www.sciencebuddies.org/
To learn more about how to choose and use appropriate laboratory equipment and tools refer to
MS TIPS Benchmark N.8.A.5
Controls and Variables
A crucial part of designing a controlled experiment is to identify the variable to be tested and the
controls needed to assure that results are due to the variable being tested and not other conditions
or influences.
Variable is the treatment or condition that is to be tested. In a controlled experiment, the
variable is the only thing that should be different between different experimental set ups. Some
texts describe both the independent and dependent variable, but it is not necessary to teach
middle school students that vocabulary. The important thing to help these students is to help
them learn that in a controlled experiment, only one variable is to be tested, and that everything
else in the experiment should remain constant.
Controls are conditions and treatments in a controlled experiment that are kept constant. To
determine if that variable affects the outcome of the experiment, a control must also be run
which entails the exact same conditions, but without the variable being tested. For example, if
we wanted to test the effect of salt water on the growth of plant X, you would water (several
samples) of plant X with the same concentration of salt water. The concentration of the salt
would remain the same throughout the experiment as would other conditions such as the amount
of water, light, temperature, etc. The control would be to run the same experiment using no salt
in the water, but keeping everything else the same.
The following chart provides examples of variables and controls. Although middle school
students do not need to learn the terms Independent Variable and Dependent Variable, the
following table illustrates examples of variables and controls.
Question
Independent Variable
Dependent Variables
Controlled Variables
(What I observe)
(What I keep the same)
(What I change)
How
much
water
flows
through a
faucet at
different
openings?
Water faucet opening
(closed, half open, fully
open)
Does
heating a
cup of
water
allow it to
dissolve
more
sugar?
Temperature of the water
measured in degrees
Centigrade
Does
fertilizer
make a
plant
grow
bigger?
Amount of fertilizer
measured in grams
Amount of water flowing measured in
liters per minute

The Faucet

Water pressure, or
how much the water
is "pushing"
"Different water pressure
might also cause different
amounts of water to flow
and different faucets may
behave differently, so to
insure a fair test I want to
keep the water pressure
and the faucet the same for
each faucet opening that I
test."
Amount of sugar that dissolves
completely measured in grams

Stirring

Type of sugar
"More stirring might also
increase the amount of
sugar that dissolves and
different sugars might
dissolve in different
amounts, so to insure a fair
test I want to keep these
variables the same for each
cup of water."
1. Growth of the plant measured

Same size pot for
each plant

Same type of plant in
each pot

Same type and
amount of soil in
each pot

Same amount of
water and light

Make measurements
of growth for each
plant at the same
time
by its height
2. Growth of the plant measured
by the number of leaves
3. See Measuring Plant Growth
for more ways to measure
plant growth
"The many variables above
can each change how fast a
plant grows, so to insure a
fair test of the fertilizer,
each of them must be kept
the same for every pot."
Does an
electric
motor
turn
faster if
you
increase
the
voltage?
Voltage of the electricity
measured in volts
Speed of rotation measured in
revolutions per minute (RPMs)

Same motor for
every test

The motor should be
doing the same work
for each test (turning
the same wheel,
propeller or
whatever)
"The work that a motor
performs has a big impact
on its speed, so to insure a
fair test I must keep that
variable the same."
Table 1. Examples of Variables and Controls
(From: http://www.sciencebuddies.org/science-fair-projects/project_variables.shtml)
For additional information on controls, see
http://www.nationmaster.com/encyclopedia/Control-experiment
Once the decision has been made as to what to test, and an experimental procedure has been
developed, the following table from Science Buddies.org can be used as a check list for the
experimental design:
What Makes a Good Experimental Procedure?
For
a
Good
Experimental
Procedure, You Should Answer
"Yes" to Every Question
Have you included a description and size for all experimental and
control groups?
Yes / No
Have you included a step-by-step list of all procedures?
Yes / No
Have you described how to the change independent variable and how
to measure that change?
Yes / No
Have you explained how to measure the resulting change in the
dependent variable or variables?
Yes / No
Have you explained how the controlled variables will be maintained
at a constant value?
Yes / No
Have you specified how many times you intend to repeat the
experiment (should be at least three times), and is that number of
repetitions sufficient to give you reliable data?
Yes / No
The ultimate test: Can another individual duplicate the experiment
based on the experimental procedure you have written?
Yes / No
If you are doing an engineering or programming project, have you
completed several preliminary designs?
Yes / No
Table 2. Procedure checklist.
(From http://www.sciencebuddies.org/science-fair-projects/project_experimental_procedure.shtml)
To learn more about designing a fair experiment, see
http://www.sciencebuddies.org/science-fair-projects/project_experimental_procedure.shtml
Data must be collected and recorded appropriately
As the controlled experiment is being conducted, data must be gathered and recorded in an
organized and thoughtful way. The data may include measurable (quantitative) and descriptive
(qualitative) observations. Tables, charts, and illustrations should be labeled completely and
clearly. Data gathered in an experiment should be organized and clear. The following three
slides are from a PowerPoint online. They illustrate the difference between good data recording
and poor data recording.
Poorly organized data
Figure 4. Poorly organized data.
(From: http://csc.gallaudet.edu/soarhigh/ReportingInvestigations.ppt#17)
Unlabeled Data
Figure 5. Unlabeled data.
(From http://csc.gallaudet.edu/soarhigh/ReportingInvestigations.ppt#18)
Clear and organized data
Figure 6. Clear and organized data.
(From http://csc.gallaudet.edu/soarhigh/ReportingInvestigations.ppt#19)
Other examples of data presentation can be found at
http://scene.asu.edu/habitat/data_present.html
Generally, students should gather quantitative data in a table format, which can then be later
graphed or charted.
For information on how to evaluate information in tables, graphs, and charts see
MS TIPS Benchmark N.8.A.1
For additional ways of organizing information see MS TIPS Benchmark N.8.A.7
In addition, to learn more about presentation of data in charts, tables, graphs and diagrams, see
http://www.unisanet.unisa.edu.au/Resources/la/QuickClicks%20Repository/LC_worksheet_table
s%20graphs.pdf
Two types of data can be recorded during an experiment: Quantitative and Qualitative.
Quantitative Data is measurable and can be recorded numerically. Examples would be height,
weight, length, time, and other measurements that can be recorded as or associated with a
number.
Qualitative Data is not specifically measurable by numbers, but is recorded as descriptions or
choices, or other observations that are not easily associated with numbers. Qualitative data could
include things such as a description of the way a plant looks as it grows. The following table
presents distinctions between qualitative and quantitative data.
Qualitative
Quantitative
"All research ultimately has
a qualitative grounding"
- Donald Campbell
"There's no such thing as qualitative
data.
Everything is either 1 or 0"
- Fred Kerlinger
The aim is a complete, detailed
description.
The aim is to classify features, count
them, and construct statistical models
in an attempt to explain what is
observed.
Researcher may only know roughly in
advance what he/she is looking for.
Researcher knows clearly in advance
what he/she is looking for.
Recommended during earlier phases
of research projects.
Recommended during latter phases of
research projects.
The design emerges as the study
unfolds.
All aspects of the study are carefully
designed before data is collected.
Researcher is the data gathering
instrument.
Researcher uses tools, such as
questionnaires or equipment to collect
numerical data.
Data is in the form of words, pictures
or objects.
Data is in the form of numbers and
statistics.
Subjective - individuals’
interpretation of events is
important ,e.g., uses participant
observation, in-depth interviews etc.
Objective – seeks precise
measurement & analysis of target
concepts, e.g., uses surveys,
questionnaires etc.
Qualitative data is more 'rich', time
consuming, and less able to be
generalized.
Quantitative data is more efficient,
able to test hypotheses, but may miss
contextual detail.
Researcher tends to become
subjectively immersed in the subject
matter.
Researcher tends to remain
objectively separated from the subject
matter.
Table 3. Qualitative v. Quantitative Data.
(The two quotes are from Miles & Huberman (1994, p. 40). Qualitative Data Analysis)
(From http://wilderdom.com/research/QualitativeVersusQuantitativeResearch.html)
Conclusions Must be Supported by the Evidence Gathered
Experimental evidence, data and observations, are what validate a hypothesis. Evidence makes
science valid or confirmed. Much evidence is needed to validate a hypothesis. If only one plant
is treated with fertilizer, and one plant is treated with no fertilizer, and the fertilizer plant dies, a
conclusion could be that fertilizer does not help a plant grow. However, if only one plant is
tested—what if that plant was diseased or had some problem before it started in the experiment?
A scientist would have to test MANY plants. Say for example if 50 plants were treated with
fertilizer and all of them except for one grew taller than those without fertilizer, one could have
confidence stating a conclusion that the fertilizer makes the plants grow taller. The one that did
not grow could have been a faulty plant.
For discussions as to how data and evidence can be interpreted differently or used to explain
results in more than one way visit MS TIPS Benchmark N.8.A.3
Inference
From results, and based on evidence, an inference can be made. An inference is a conclusion
based only on what is observed or learned during the scientific experiment. A conclusion is a
tentative answer to the original question. This conclusion should either support or not support
the hypothesis and must be based on evidence gathered in the experiment. Any data,
observations, or evidence used to support a conclusion must be based on fact and not opinion.
To learn more about how to evaluate information to distinguish between fact and opinion visit
MS TIPS Benchmark N.8.A.2
Performance Benchmark N.8.A.4
Students know how to design and conduct a controlled experiment E/L
Common misconceptions associated with this benchmark
1. Some students think that “The Scientific Method” is the only correct way to do science
investigations.
This is a danger of teaching the scientific method. It is important to teach students inquiry as
a process, and use scientific method as ONE of many tools in the science classroom. “The
Scientific Method” is sometimes used by scientists to test hypothesis. It is taught in many
classes, described online, and can be a useful tool to teach young scientists. However, a
teacher needs to be careful not to mislead students into believing that this is the only method
of science. Science fair projects and scientific publications can contribute to an ongoing
perpetuation of this misconception, because this is the way that scientific studies are often
presented. In reality there is no one set method that scientists use universally. Scientists
approach solving problems with perseverance, creativity, prior knowledge, and repeated
testing.
Some examples of experiments including controlled experiments as well as others can be
read at http://www.kids.net.au/encyclopedia-wiki/ex/Experiment#Controlled_Experiments
2. Middle school students may think experiments are a way to produce a desired outcome,
rather than a way of testing ideas.
Students are often given “cookbook” type experiments where the steps are already written for
them and controls are already identified. If the experiment does not turn out the expected
way, students think they did something wrong. Therefore, it is necessary that students are
given many opportunities to design their own experiments and defend their conclusions with
evidence acquired. As students experience more inquiry-based activities and labs, they will
develop inquiry skills as well as the ability to identify controls, errors, and successes in
experimental designs. Inquiry can be encouraged by sometimes modifying standard text book
verification labs.
To learn how to convert standard labs into more inquiry-based experiences, see the following
two resources
http://www.tvdsb.on.ca/currscisecondary/srhs/converting%20cookbook%20labs.pdf
http://mickelson.nsta.org/Shared%20Documents/Reforming%20Cookbook%20Labs.pdf
Performance Benchmark N.8.A.4
Students know how to design and conduct a controlled experiment E/L
Sample Test Questions
Questions and Answers to come in separate file
Performance Benchmark N.8.A.4
Students know how to design and conduct a controlled experiment E/L
Answers to Sample Test Questions
Questions and Answers to come in separate file
Performance Benchmark N.8.A.4
Students know how to design and conduct a controlled experiment E/L
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. Spontaneous Generation from Science NetLinks
A lesson that demonstrates that scientific knowledge is stable, but also prone to change. This
takes students through the historical scientific studies that led to refutation of spontaneous
generation.
To access this lesson visit
http://www.sciencenetlinks.com/lessons.cfm?DocID=126
2. Scientific Method – A mini lab from Time for Kids
This mini lesson uses a timeforkids.com news article to help students learn how to identify
problems and write hypotheses.
To access this lesson, visit
http://www.timeforkids.com/TFK/teachers/minilessons/wr/0,28171,1658109,00.html
3. Biology4 Kids Quiz: The Scientific Method
An online quiz regarding various parts of a scientific method. Students can take the quiz
online and receive immediate feedback on each question. This quiz can be completed by
individual students, or projected and used with the whole class.
To access this online quiz, visit
http://www.biology4kids.com/extras/quiz_studyscimeth/index.html
4. Science Fair Central: A Soup to Nuts Handbook
This site is designed as a resource for science fair projects. Whether or not a teacher has
students participating in a science fair, this site provides excellent explanations that teachers
can use when teaching science processes.
To access this site, visit
http://school.discoveryeducation.com/sciencefaircentral/scifairstudio/handbook/scientificmet
hod.html#research
5. Independent Investigation – a graphic organizer
For a simple worksheet that can be used to help students design an experiment, visit
http://sciencespot.net/Media/indinvest.pdf
6. How Scientists Work: The Scientific Method
This site from howstuffworks.com, provides a series of short videos that provide examples of
scientific method and controlled study steps. These are all short clips that can be used as
examples in the class. There are short commercials before some of the clips. Click on the
“Related Videos” tab to access all of the video clips.
To access the video clips, visit
http://videos.howstuffworks.com/hsw/16752-how-scientists-work-the-scientific-methodvideo.htm
7. Experimental Design from Study Stack
This site has various games and game-like activities that can be used to reinforce the
vocabulary associated with controlled studies. This site includes matching, hangman,
crossword, flashcards, and more. Some of the vocabulary may be beyond the scope of
middle school science, but the students will enjoy the games as they learn!
To access the games, visit
http://www.studystack.com/menu-1924