Lines of Symmetry | Mystery Detective Worksheets | Grades 3–4 | Complete the Figure

Lines of symmetry worksheets, complete the symmetrical figure activities and mirror image reflection practice for 3rd grade and 4th grade are all included in this printable geometry Mini Mystery Detective pack of math worksheets. Students look at half a figure shaded on a grid, flip it across the dashed line of symmetry — the fold line, the mirror line — and count the squares in the whole finished shape. It is the reflection half of a flips, slides and turns unit, drawn on grid paper so symmetry can be counted as well as seen. No cutting, no gluing, no technology, and completely no prep — just print and go.

Nothing in this pack is seasonal, so it drops into your year wherever symmetry lands: a 2D shapes and geometry unit, a transformations and reflections lesson, spring test prep, or end-of-year review. Use it for math centers and stations, morning work and bell ringers, fast finishers, small group and intervention, homework, or a day you need something a substitute can hand out cold. Black and white, ink friendly, PDF, with a full answer key for every case.

What's Inside

• Completing a symmetrical figure across a vertical line of symmetry, then counting every square in the finished shape
• Completing a figure across a horizontal line of symmetry, so students reflect up and down as well as side to side
• Reflecting a figure that sits on the right of the fold, so the reflection runs the other way — the half of symmetry a left-only worksheet never asks for
• Spotting the squares that have no matching square yet on a figure somebody started copying and left half finished
• A final mixed case where the line of symmetry can run down the grid or across it, with the shaded half on either side
• Counting squares in a figure to find its total, so the geometry doubles as unit-square area practice
• Full answer keys for every case, with the completed symmetrical figure shaded in on the grid — not just the number, so students can see exactly where a count went wrong

Five cases to crack: The Mirror Mural, The Missing Halves, The Flipped Lab Tray, The Backwards Banner and The Canteen Cut-Outs.

What is a Mini Mystery Detective?

A no-prep detective activity where students solve math problems to cross off suspects and unmask the culprit. Skill practice plus critical thinking in one engaging, self-checking worksheet set — an escape room without the locks, boxes or setup.

When to Use This Resource

• Geometry, 2D shapes and transformations units
• Reflections, flips and mirror image lessons
• Math centers, stations and rotations
• Morning work and bell ringers
• Fast finishers and independent work
• Sub days — a substitute can hand it out cold
• Homework and extra practice
• Small group, RTI and intervention
• Spiral review, test prep and end-of-year revision

Grade Levels

Designed for 3rd grade and 4th grade, and used across upper elementary. The cases get harder as they go, so the same pack scaffolds struggling 5th graders and stretches confident 2nd graders. The grid means it also works for ELL and ESL students and for special education, RTI and intervention groups — nothing has to be read to be solved.

Why Teachers Love Mystery Detectives

• Zero prep — print and hand out. No cutting, no gluing, no technology, no laminating
• Self-checking: a correct page leaves exactly one suspect standing, so students catch their own mistakes
• The detective hook keeps students working through a full page of geometry
• Every figure sits on a grid, so students who cannot yet picture a reflection can count their way to it
• Black and white and ink friendly — it photocopies cleanly
• Answer keys that show the finished figure drawn in, so marking takes seconds and students can self-correct

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