Addition & Skip Counting CSI Mystery Worksheets | Grades 3–6 | The Number on the Loose

August CSI math worksheets for 4th grade math review that stretches to 3rd grade and 5th grade: hundreds chart puzzles, skip counting and multiples of 4, run as a CSI Mystery Detective case where the suspect happens to be a number. Nobody can say which one, so the class runs a real investigation: evidence, forensics, line-up, interrogation, with every stage taking more numbers off the board. Supplied ready to print in color and black-and-white versions. Students decode a cipher, shade every multiple of 4, skip count in twenties to check the witness numbers and finish on a shading puzzle that closes the mystery.

The Case: The Suspect Number

There is a number at the center of this and nobody can say which one. Your students run it as a real investigation: find the evidence, do the forensics, put the survivors in a line-up, then interrogate the last two. Every stage takes more numbers off the board. The final puzzle is the one that gets a confession.

What's Inside

• A letter-and-number cipher that decodes the opening message
• Shading all the multiples of 4 on a hundreds chart
• Skip counting in twenties to check the witness numbers
• Cross-matching the evidence so far to narrow the suspect list
• A final shading puzzle that separates the last two suspects
• Full color and black-and-white versions of every page
• Answer keys for the whole case

What Is a CSI Mystery Detective Case?

Every CSI Mystery Detective case runs on the same engine: solve, eliminate, repeat. The class is handed a case and a page of math worksheets, and the answers rule candidates out one by one until a single one is left. It is a math escape room without locks, apps or preparation of any kind. Because the deduction only closes on correct arithmetic, detective activities get checked by the student rather than by you. As a math activity it fills a lesson, sits in math centers, or runs itself as a sub plan.

When to Use This Resource

• Skip counting and multiples practice with a purpose behind it
• Hundreds chart work that is not coloring for its own sake
• Math centers, early finishers and independent work
• Emergency sub plans that run themselves
• Back-to-school weeks and end of year review

Grade Levels

Built for 3rd grade, 4th grade and 5th grade. Third graders usually want the hundreds chart explained once before starting; fourth and fifth graders run the investigation independently. It also suits 2nd grade students who are ahead on skip counting and ready for something longer.

Why Teachers Love CSI Mystery Detective Cases

• Zero prep - print and hand out
• Self-checking by design, because an early error shows up later
• Number work students will actually finish
• Works as a whole lesson, a center, or a filler for an awkward afternoon

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