Go Math! Grade 1, Chapter 12: Two-Dimensional Geometry
In this unit, first graders finish the year with flat, two-dimensional shapes. They sort shapes by sides and vertices, the corners, combine them to make new shapes, and split circles and rectangles into equal shares called halves and fourths. After solid shapes in the last unit, this looks at the flat faces those solids are made from, and how flat shapes fit together.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Chapter 12?
- Naming triangles, squares, rectangles, trapezoids, and hexagons by counting their straight sides and vertices. Learn more: What makes a triangle a triangle
- Combining flat shapes, like two trapezoids into a hexagon, and building new shapes from those combinations. Learn more: Building bigger shapes from smaller ones
- Partitioning circles and rectangles into two and four equal shares, called halves, fourths, and quarters. Learn more: Halves and quarters of circles and rectangles
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
What must be true for a shape to be a triangle?
- It must have 3 straight sides.
- It must be blue.
- It must be big.
How you can help
- Draw shapes in different sizes and turned different ways, and ask your child to name each one by counting its sides and corners.
- Cut a paper square and a paper circle into halves and then fourths, and ask your child to fit them back together into the whole.
- Share a granola bar or a tortilla by breaking it into two equal halves, and ask how your child knows each person got the same amount.
Where kids can get stuck
- Naming a shape a triangle even though one of its sides is curved.
- Missing a familiar shape built from smaller ones, like two triangles making a square.
- Believing a fourth is bigger than a half because 4 is bigger than 2.
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
- two-dimensional
- Flat, like a drawing of a square or circle.
- side
- A straight line that makes part of a shape's edge.
- vertex
- A corner, where two sides of a shape meet.
- trapezoid
- A four-sided shape with one pair of sides that run the same way.
- hexagon
- A closed shape with 6 straight sides and 6 corners.
- equal shares
- Parts of a whole that are all the same size.
- half
- One of two equal parts of a whole.
- fourth
- One of four equal parts of a whole, also called a quarter.
- quarter
- Another name for a fourth, one of four equal parts.
Ready to build your child’s confidence with flat shapes and halves?
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.
Join the club
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 Go Math! Grade 1 Chapter 12 cover?
Go Math! Grade 1 Chapter 12 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.