4.6.B
The Standard
identify and draw one or more lines of symmetry, if they exist, for a two-dimensional figure
Texas Essential Knowledge and Skills for Mathematics
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students decide whether a flat figure can be folded into two matching halves. They draw every fold line that works and recognize when no such line exists.
What Mastery Looks Like
- Students correctly mark all matching fold lines on regular, irregular, and rotated figures. They verify each choice by showing that corresponding edges and corners align.
Common Misconceptions
- Students may think any line that splits a figure into equal areas works, even when the halves do not match. They may miss diagonal symmetry or assume every figure has exactly one matching fold.
How to Assess It
- Give students a square, a scalene triangle, and an isosceles triangle. Ask them to draw every matching fold line or write “none.”
Lesson moves
Ways to Teach It
Give pairs paper shapes to cut, fold, and trace each crease where both halves match exactly.
Show a square and a non-square rectangle, then ask students to write why their numbers of matching fold lines differ.
Play a card sort where students group figures by zero, one, two, or more matching fold lines.
Have students photograph classroom logos or objects, then mark possible matching fold lines on printed copies.
Keep exploring
Related Standards
- 1.6.G
partition two-dimensional figures into two and four fair shares or equal parts and describe the parts using words
- 2.8.E
decompose two-dimensional shapes such as cutting out a square from a rectangle, dividing a shape in half, or partitioning a rectangle into identical triangles a...
- 1.6.C
create two-dimensional figures, including circles, triangles, rectangles, and squares, as special rectangles, rhombuses, and hexagons
- 4.6.D
classify two-dimensional figures based on the presence or absence of parallel or perpendicular lines or the presence or absence of angles of a specified size
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