1. MD.A.2
Express the length of an object as a whole number of length units, by laying multiple copies of a shorter object (the length unit) end to end; understand that the length measurement of an object is the number
of same-size length units that span it with no gaps or overlaps. Limit to contexts where the object being measured is spanned by a whole number
of length units with no gaps or overlaps.
Unpacked
This standard focuses on the student’s ability to understand the concept of measuring the length of an object from end to end using objects. The student will measure lengths that are a whole number of length units, where the length unit is some shorter object (e.g., using paper clips, unifix cubes, chain links, etc). Students need to have a wide variety of experiences with handson activities that allow them to manipulate the objects being measured.
According to the CCSS for Math, students develop an understanding of the meaning and processes of measurement, including underlying concepts such as iterating (the mental activity of building up the length of an object with equal-sized units) and the transitivity principle for indirect measurement.
(If the length of object A is greater than the length of object B, and the length of object B is greater than the length of object C, then the length of object A is greater than the length of object C. This principle applies to measurement of other quantities as well.)
This standard asks students to use multiple copies of one object to measure a larger object. This concept, stated above, is referred to as iteration . Through numerous experiences and careful questioning by the teacher, students will recognize the importance of making sure that there are not any gaps or overlaps in order to get an accurate measurement. This concept is a foundational building block for the concept of area in 3 rd grade.

Notice that this standard does not mention standard measurement units, such as inches and centimeters, nor does it mention conventional measuring tools, such as rulers or tape measures. The emphasis of this standard is for the student to determine how many of a specified unit (e.g., paper clips, connecting cubes, etc.) it takes to span the length of the object being measured. Teachers should stress the importance of making sure there are no gaps or overlaps when measuring. In future use of rulers and tape measures, students must have a foundational understanding that 12 inches on a ruler is the same as if there were 12 inch-sized units lying end to end. At this stage of development, it is important that students actually lay the units end to end and count the total used to make that connection.
Some measures will not be an exact unit. The length may fall in the middle of a unit. Students will need to adjust their answers to this fact and choose the closer number. They must also explore how to align the object to the tool used to measure.
Questions to Focus Instruction:
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How do I know my students understand that length is measurement of an object from one end to another?
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Are my students accurately measuring an object?
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Are there gaps between the objects or are they overlapping?
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Have my students begun measuring at the starting point and ended measuring at the end point of the object?
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What objects whose lengths are a whole number multiple of the length of a reference object can be provided to students?
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Are students able to use a reference object to correctly measure the length of a larger object, by placing copies of the reference object end-to-end with no overlap and no gaps?
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What activities and opportunities can I provide that will allow students practice with using smaller objects to measure the length of a larger object?

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How can I use manipulatives and other technologies that will allow for direct, hands-on exploration of measuring the length of objects?