Illustrative Mathematics Grade 4, Unit 8: Properties of Two-Dimensional Shapes
In this unit, your child sorts two-dimensional shapes by their properties: parallel sides, perpendicular sides, and the size of their angles. They identify right triangles and find lines of symmetry. It builds on last unit's lines and angles, and leads into the final unit, which pulls the year's skills together.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 8?
- Sorting triangles and quadrilaterals by parallel sides, perpendicular sides, and acute, right, or obtuse angles. Learn more: Sorting shapes by their sides and angles
- Finding lines of symmetry by folding and drawing, and completing shapes so they're symmetric. Learn more: Finding lines of symmetry
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
Sofia draws a triangle with angles of 90°, 50° and 40°. What kind of triangle is it?
- An obtuse triangle
- A right triangle
- An acute triangle
How you can help
- Sort road signs or shapes on boxes during a walk or ride. Ask your child which have parallel sides and which have a right angle. A box flap has both; a yield sign has neither.
- Fold paper shapes or napkins and ask your child to predict where the halves will match, then fold to check, trying the middle and the diagonals.
- Draw a four-sided shape and ask your child to name everything it has: parallel sides, right angles, and lines of symmetry. Then turn it and ask if anything changed.
Where kids can get stuck
- Leaving a square out of the rectangles and parallelograms, because it already has its own name.
- Deciding two sides are parallel just because they don't cross on the page yet.
- Stopping after one line of symmetry on a square, which has four.
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
- parallel lines
- Lines that always stay the same distance apart and never meet.
- perpendicular lines
- Lines that meet or cross to make right angles.
- right triangle
- A triangle with one right angle.
- classify
- To sort shapes into groups by what they have in common.
- quadrilateral
- A flat shape with four straight sides.
- trapezoid
- A quadrilateral with at least one pair of parallel sides.
- parallelogram
- A quadrilateral with two pairs of parallel sides.
- line of symmetry
- A line that folds a shape into two halves that match exactly.
Ready to build your child’s confidence with shapes and symmetry?
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 Illustrative Mathematics Grade 4 Unit 8 cover?
Illustrative Mathematics Grade 4 Unit 8 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.