Christmas Addition & Subtraction CSI Mystery

Inside the case file

December Christmas CSI math worksheets on addition and subtraction, wrapped around a Secret Santa mystery the class will want solved. One gift out of the hat was not what it should have been, and nobody will own up. Made for 2nd grade and 3rd grade, this CSI Mystery Detective case works two-digit and three-digit addition and subtraction, and each correct answer strikes one suspect from the list until only the guilty gift-giver is left. Christmas math activities that need nothing but a printer, in color or black-and-white, with answer keys. Students decode a map key, follow an addition path where odd or even settles the clue, and work subtraction through a letter key.

The Case: Secret Santa

That time of year has come round again. Everyone has a bit of a skip in their step, a smile for strangers, an extra hug for relatives they see once a decade. Even Mrs McPuffers has gone soft. The Secret Santa names went into the hat, the gifts came out, and one of them was not what it should have been. Nobody will own up, so your students will have to work out who it was.

What's Inside

• Reading letters off a map with a key to decode the first clue
• Addition along a path where an odd or even final total decides the answer
• Addition problems used to color the correct arrow forward
• Three-digit addition decoded through a letter key
• Subtraction worked through a key to reveal the final clue
• Full color and black-and-white versions of every page
• Answer keys for the whole case

What Is a CSI Mystery Detective Case?

The format never changes: a crime, a line-up of suspects, and math that decides which of them it cannot be. A CSI Mystery Detective case is a math escape room that needs a printer instead of locks, an app or any setup. It beats a stack of math worksheets on the same content for one reason - a wrong answer breaks the deduction loudly, so students go back over their own work. It fills a whole lesson, sits in math centers, or works as detective activities for early finishers.

When to Use This Resource

• The last weeks of December, when a normal worksheet will not hold them
• Class Secret Santa week, alongside the real thing
• Math centers, early finishers and independent work
• Emergency sub plans that run themselves
• Whole-class detective sessions, small groups or partner work

Grade Levels

Built for 2nd grade and 3rd grade. Second graders usually work the three-digit pages in pairs; third graders run the case independently inside a lesson. It also suits 4th grade students who need addition and subtraction review in a form that does not feel like going backwards.

Why Teachers Love CSI Mystery Detective Cases

• Zero prep - print and hand out
• Self-checking by design, because a wrong answer breaks the deduction
• A December activity that still does real math
• Works as a whole lesson, a center, or a filler for an awkward afternoon

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