Primary Standards:
MAFS.1.MD.1.1 Order three objects by length; compare the lengths of two objects indirectly by using a third object.
MAFS.1.MD.1.a Understand how to use a ruler to measure length to the nearest inch:
- Recognize that the ruler is a tool that can be used to measure the attribute of length.
- Understand the importance of the zero point and endpoint and that the length measure is the span between two points.
- Recognize that the units marked on a ruler have equal length intervals and fit together with no gaps or overlaps. These equal interval distances can be counted to determine the overall length of an object.
Content Knowledge:
First grade builds upon students understanding of length and comparisons in kindergarten. Students directly compared two objects lengths, focusing on conventions such as lining up the end points of each object. In first grade, students will now directly compare three objects, and indirectly compare two objects using the length of a third object as a benchmark (applying the transitive property).
In kindergarten students experienced length as a distance from one point to another. They realized length is measured in a number of equal sized units, iterated (laid end-to-end) with no gaps or overlaps. In first grade, students will come to recognize that a ruler is a measuring tool and a model of this concept. It is a model of equal sized units, laid end-to-end, with numbers corresponding to the end point of each unit (in this case the unit will be inches). The ruler is a short cut to having to lay out many inch markers end-to-end and having to count them all. Students will also use this tool to then measure lengths of objects to the nearest inch, with an understanding that the object’s end point should be placed at the zero-point of the ruler, not always the end of the ruler, and that the number on the ruler counts the number of units (inches).
It should not be assumed students have a concept of an inch as a unit of measurement. To help students develop this understanding, they can use inch tiles, and strips of card stock cut to inch long segments. Opportunities for first grade students to investigate these measurement concepts provide the foundations for more complex measurement skills in the future, and connecting to use different units such as feet, yards, and metric units in 2nd grade.
GCG 1 – Learning Goal: As a Mathematician, I will be able to Compare and Order Length
- Step 1: Compare the Length of Two Objects using the same units and the language: longer, taller, shorter
- Step 2: Order three objects by shortest to longest length (including using non-standard units to order)
- Step 3: Compare the length of two objects by using a third object
GCG 2 – Learning Goal: As a Mathematician, I will be able to Estimate and Measure Length using an Inch Ruler