4th Grade · Geometry
4.G.A.3: Find lines of symmetry, where a shape folds into matching halves
4.G.A.3 is a 4th 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
Recognize a line of symmetry for a two-dimensional figure as a line across the figure such that the figure can be folded along the line into matching parts. Identify line-symmetric figures and draw lines of symmetry.
In plain words
Find lines of symmetry, where a shape folds into matching halves.
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
Can this shape be folded straight across its middle, top half onto bottom half, so the two halves match?
- No, its top side is shorter than its bottom side.
- Yes, because it has four sides.
- Yes, its top and bottom sides are parallel.
Where students can get stuck
- Drawing a rectangle's diagonal as a line of symmetry, because it makes two equal pieces, even though the halves do not match when folded.
- Stopping after one line of symmetry on a shape with several, such as the vertical line on a square.
- Missing a line of symmetry when a shape is tilted on the page, as if it must stand upright.
Effective teaching strategies
- Cut out a rectangle that is longer than it is wide and fold it along a diagonal and again through the midpoints of opposite sides, and ask which fold makes matching halves.
- Have students fold a paper square every way that makes matching halves, and find all four lines of symmetry, two through the sides and two diagonals.
- Give students shapes drawn tilted on the page and have them fold or trace to find the lines of symmetry, so they see the lines turn with the shape.
Units that teach this standard
Find where 4.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
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 Finding lines of symmetry 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.