Illustrative Mathematics Grade 1, Unit 6: Length Measurements Within 120
In this unit, first graders compare and order lengths and measure objects with length units laid end to end, with no gaps or overlaps. Because measurements can be long, they also count, read, and write numbers all the way to 120. It builds on adding within 100 from the last unit, and next they study shapes and telling time.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 6?
- Counting, reading, and writing numbers to 120, often while recording how many units long something is. Learn more: Counting, reading, and writing numbers to 120
- Ordering three objects from shortest to longest and comparing two lengths by measuring each with the same thing. Learn more: Ordering three things from shortest to longest
- Measuring with same-size units, like cubes or paper clips, end to end, and counting how many units long. Learn more: Measuring length by lining up same-size objects
Sample questions to try together
These are real questions from our practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
Count by tens: 10, 20, 30, 40, __. What number comes next?
- 51
- 50
- 60
How you can help
- Measure the length of a hallway or rug in your child's footsteps, heel to toe, and count together, going past 100 if you can.
- Line up three things, like a spoon, a pencil, and a remote, and ask your child to order them from shortest to longest with their ends together.
- Measure a table with spoons laid end to end, then check together for gaps and overlaps. Write the number of spoons down.
Where kids can get stuck
- Counting past 100 as "100, 200, 300" while measuring something long.
- Overlapping or leaving gaps between units, so the count isn't the true length.
- Deciding which object is longest without lining up their ends first.
Practice makes perfect
Bobby's Math Club has practice problems that adapt to your child’s level, each with a detailed explanation and an easy-to-follow video, so your child can build confidence in these skills one step at a time.
Words your child will hear
- length
- How long something is from one end to the other.
- unit
- A same-size thing used to measure, like a paper clip or a cube.
- measure
- Find out how long something is by counting units.
- longer
- Having more length than something else.
- shorter
- Having less length than something else.
- gap
- An empty space between units, which makes a measurement wrong.
- overlap
- When units lie on top of each other, which makes a measurement wrong.
- numeral
- The written symbol for a number, like 25.
- hundred
- Ten tens, written 100.
Want to help your child master measuring and counting to 120?
In Bobby's Math Club, your child practices these skills at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free.
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Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
Which math standards does Illustrative Mathematics Grade 1 Unit 6 cover?
Illustrative Mathematics Grade 1 Unit 6 covers these math standards. Each one links to what it means, sample questions, and teaching strategies.
For teachers: Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence. Learn how Bobby's Math Club can help your students grow.