Skip Counting & Addition CSI Mystery Worksheets

Inside the case file

3rd grade, 4th grade and 5th grade math review of multiples, factors and skip counting, run as a CSI Mystery Detective case that fits January, when classes need a restart after the break. A number is guilty and nobody knows which one, so students work it like a real investigation - evidence, forensics, line-up, interrogation - and every stage rules more numbers out. These CSI math worksheets turn a hundreds chart into the crime scene, and the mystery only closes when the last two suspects are separated by one final puzzle. Print and go. Students crack a letter-and-number cipher, shade the multiples of 3 and 4, and cross-match witness numbers against the evidence. Answer keys included.

The Case: The Suspect Number

A number has done something, and nobody knows which one. Your students work it the way a real investigation works: evidence first, then forensics, then a line-up, then interrogation. Every stage rules more numbers out. By the end there are two left, both claiming innocence, and one puzzle standing between your class and a confession.

What's Inside

• A letter-and-number cipher that decodes the opening message
• Shading all the multiples of 3 and 4 on a hundreds chart
• Narrowing the suspects to numbers that are multiples of both
• Cross-matching witness numbers against the evidence so far
• 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?

A CSI Mystery Detective case is what a math escape room becomes when the locks come off and the deduction stays. Students solve, cross a name off the line-up, and keep narrowing until one is left. Nothing to cut, nothing to install, nothing to prepare. Unlike ordinary math worksheets it cannot be drifted through, because an error leaves more than one candidate standing and the class sees it immediately. A math activity that fills a lesson, suits math centers, and works as detective activities for early finishers.

When to Use This Resource

• Introducing or consolidating multiples and factors
• Hundreds chart and skip counting work with a purpose behind it
• 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 need the hundreds chart talked through once before they start; fourth and fifth graders run the whole investigation independently. It also gives 6th grade students who are shaky on factors a way to rebuild without going back to a worksheet.

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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