Addition & Subtraction CSI Mystery Worksheets
Grades 2–3 · Alien Invasion
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Inside the case file
CSI Mystery Detective goes interplanetary: an alien invasion that 2nd grade and 3rd grade students solve with addition, subtraction and rounding, where only correct answers reveal which alien is behind it. It begins as an ordinary September school day with a dot growing bigger on the horizon, and ends with students working two-digit and three-digit addition, rounding to the nearest ten and cracking a number sequence to shrink the suspect line-up. These CSI math worksheets come in full color and black and white with answer keys, ready the moment they leave the printer. Students spot wrong answers, keep a tally, follow linked clues and cross off suspects until one alien remains in the mystery.
The Case: Alien Invasion
It starts as an ordinary school day. Your students are at their desks, looking out at a calm sky, when a tiny dot appears on the horizon and starts getting bigger. By the time anyone thinks to shout, it is close enough to see clearly, and the school day is over. Somewhere out there is one alien responsible for all of this, and the only way to identify it is to work the math and narrow the field.
What's Inside
- Spotting correct and incorrect answers and marking them off against a tally
- Two-digit and three-digit addition worked through a chain of linked clues
- Rounding numbers to the nearest ten to shade the right answer
- A number sequence puzzle that builds to one final figure
- A suspect line-up that narrows every time a clue is solved
- 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 a printable investigation your class solves with math. It runs like a math escape room with the locks taken out - no app, no props, no prep - and rather than opening a box, every correct answer rules one suspect out of the line-up until a single name is left. That is the difference between detective activities and ordinary math worksheets: the arithmetic decides the outcome, so students check their own work before they hand it in. As a math activity it fills a lesson, a center, or a sub plan.
When to Use This Resource
- Back-to-school weeks, when you want the math to feel like fun rather than testing
- Math centers, early finishers and independent work
- Emergency sub plans that run themselves
- End of year review, when attention is thin and the work still has to happen
- Whole-class detective sessions, small groups or partner work
Grade Levels
Built for 2nd grade and 3rd grade. Second graders usually work it in pairs and take their time over the three-digit addition; third graders can run the case independently and finish inside a lesson. It also suits 4th grade students who need addition, subtraction and rounding review in a form that does not look like remedial work.
Why Teachers Love CSI Mystery Detective Cases
- Zero prep - print and hand out
- Self-checking by design, because a wrong answer breaks the deduction
- Repeatable practice students ask to do again
- Works as a whole lesson, a center, or a filler for an awkward afternoon
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