1st Grade · Geometry
1.G.A.2: Compose two-dimensional shapes or three-dimensional shapes
1.G.A.2 is a 1st grade Common Core math standard in Geometry. Here’s what it really covers, and how you can help your students learn it.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
The standard
Compose two-dimensional shapes (rectangles, squares, trapezoids, triangles, half-circles, and quarter-circles) or three-dimensional shapes (cubes, right rectangular prisms, right circular cones, and right circular cylinders) to create a composite shape, and compose new shapes from the composite shape.
In plain words
Compose two-dimensional shapes or three-dimensional shapes.
Sample questions from student practice
These questions from Bobby's Math Club are the kinds of questions your students will see. You can try answering them to see what a student might see.
Question 1 of 3
If you cut a rectangle exactly in half straight down the middle, what two shapes do you make?
- Rectangles
- Circles
- Triangles
Where students can get stuck
- Overlapping shapes or leaving gaps between them, then being unsure what new shape has been made.
- Missing a familiar shape once it is built from smaller pieces, like not seeing that two triangles make a square.
- Naming a combined shape after its pieces, calling a rectangle made of two squares "two squares."
Effective teaching strategies
- Give students two same-size paper triangles with a square corner and ask them to join the triangles along a full side, with no gaps or overlaps, into a larger shape such as a square or a rectangle.
- Ask students to build a rectangle from two squares, then name the new shape as a rectangle and say what the pieces were.
- Stack three cubes face to face and ask students to name the new solid they built, a rectangular prism, and tell how it differs from one cube.
Units that teach this standard
Find where 1.G.A.2 lands in the program you teach. Each unit has a guide written for families. Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence.
Bridges in Mathematics
enVision Mathematics
Everyday Mathematics
Go Math!
i-Ready Classroom Mathematics
Illustrative Mathematics
Into Math
Math Expressions
Reveal Math
Don’t see your curriculum? Contact Bobby and we’ll see if we can help!
Share it with families
Families can read Building bigger shapes from smaller ones for a plain-language look at this skill, with three questions to try together and ideas for helping at home.
Help every student practice geometry at home
In Bobby's Math Club, students practice 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 for every family.
See how it works for teachers
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.