Kindergarten · Geometry
K.G.A.3: Identify shapes as 2D or 3D
K.G.A.3 is a kindergarten 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
Identify shapes as two-dimensional (lying in a plane, "flat") or three-dimensional ("solid").
In plain words
Identify shapes as 2D or 3D.
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
Look at this shape. Is it a flat shape or a solid shape?
- A solid shape
- A round shape
- A flat shape
Where students can get stuck
- Calling a ball a circle or a block a square, using a flat name because that is how it looks from one side.
- Treating a paper plate or a coin as a flat shape, not seeing that it is a very thin solid.
- Sorting shapes by color or size instead of by whether they are flat or solid.
Effective teaching strategies
- Hold a ball beside a paper circle and ask which one rolls and which one lies flat on the table, so flat and solid connect to what hands can do.
- Pass around a ball and a cube-shaped block and use the words sphere and cube, so students name solid things as solids and not as a circle or a square.
- Have students sort a mix of paper cutouts and solid blocks into flat and solid groups, even when the colors match, so color and size do not decide the sort.
Units that teach this standard
Find where K.G.A.3 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
Eureka Math
Everyday Mathematics
Go Math!
i-Ready Classroom Mathematics
Illustrative Mathematics
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 Telling flat shapes from solid shapes 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.