Math Expressions Grade 4, Unit 8: Geometry
In this unit, your child studies lines, rays, angles, and shapes: measuring and drawing angles with a protractor, finding missing angles, sorting shapes by parallel and perpendicular sides, and drawing lines of symmetry. It follows the work on fractions and decimals, which shows up again in fractions of a turn, and finishes the year with hands-on geometry.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 8?
- Drawing and labeling points, lines, rays, and line segments, and identifying parallel and perpendicular lines inside shapes. Learn more: Spotting lines, rays, angles, and parallel lines
- Grouping triangles and quadrilaterals by their sides and angles, including right triangles, trapezoids, and parallelograms. Learn more: Sorting shapes by their sides and angles
- Finding and drawing lines of symmetry, where a shape folds into two matching halves, and noticing shapes with several of them. Learn more: Finding lines of symmetry
- Understanding that an angle measures a turn, with 1 degree being 1/360 of a full circle. Learn more: What angles are and how degrees measure them
- Using a protractor to measure angles to the nearest degree, and to draw angles of a given size. Learn more: Measuring and drawing angles with a protractor
- Adding angle measures that sit side by side, and subtracting to find a missing angle inside a right or straight angle. Learn more: Adding angles together to find a missing one
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
How many endpoints does a line segment have?
- Two
- One
- Zero
How you can help
- Fold paper shapes, such as a square, a heart, and a rectangle, and ask your child to find every fold where the two halves match exactly.
- Open a door or a book to different widths and ask whether each angle is acute, right, or obtuse, then estimate its size in degrees.
- Draw a right angle split into two parts, label one part 35 degrees, and ask your child to find the other part without measuring.
Where kids can get stuck
- Drawing a rectangle's diagonal as a line of symmetry, even though the two halves don't match when folded.
- Placing the protractor's edge at the vertex instead of its center point, which throws off every reading.
- Subtracting from 180 instead of 90 to find the missing part of a right angle.
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
- ray
- Part of a line with one endpoint that goes on forever in one direction.
- line segment
- Part of a line with two endpoints.
- parallel lines
- Lines that stay the same distance apart and never meet.
- perpendicular lines
- Lines that cross or meet to form right angles.
- degree
- The unit for measuring angles; a full turn is 360 degrees.
- protractor
- A tool for measuring and drawing angles in degrees.
- right triangle
- A triangle with one right angle.
- line of symmetry
- A line that folds a shape into two halves that match exactly.
- vertex
- The point where the two rays of an angle meet.
Want to help your child master angles and shapes?
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.
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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 Math Expressions Grade 4 Unit 8 cover?
Math Expressions Grade 4 Unit 8 covers these math standards. Each one links to what it means, sample questions, and teaching strategies.
- 4.G.A.1: Name rays and angles, and spot parallel and perpendicular lines.
- 4.G.A.2: Sort shapes by their parallel sides and right angles.
- 4.G.A.3: Find lines of symmetry, where a shape folds into matching halves.
- 4.MD.C.5: Understand angles as turns measured in degrees: a full turn is 360°.
- 4.MD.C.6: Measure angles in degrees with a protractor.
- 4.MD.C.7: Add angles together, and find a missing angle.
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.