Back to School 3 Digit Addition with Regrouping Math Detective Mystery
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Inside the case file
3 digit addition with regrouping worksheets for 3rd grade and 4th grade, three CSI Mini Mystery Detective math cases set in school for the first weeks back. Regrouping is needed across the tens and the hundreds on every sum, and each correct total crosses a suspect off the lineup, so the page checks itself. Back to school math activities for August and September, then math centers, early finishers, homework, morning work, test prep and sub plans, print and go with full answer keys.
The first weeks of third grade are for finding out what stuck over the summer, and a CSI Mini Mystery Detective math case file does that without putting a test in front of anyone. Students add, match the total to a suspect and cross the name off, so the ones who have lost their regrouping show up on the lineup rather than on a mark sheet. Three cases, three mornings, no prep.
The Cases
- The Teachers Lunchbox - gone, and nobody saw a thing
- The Missing Teacher - a teacher has disappeared
- The Missing Art Supplies - the art cupboard is emptied
What's Inside
- Three case files, each with a crime sheet and its own lineup of suspects
- Three digit addition with regrouping on every page
- Regrouping needed across the tens and the hundreds, not just once per sum
- Each answer matches one suspect and no other, so the page checks itself
- A full answer key for every case
- Print and go: no cutting, no laminating, nothing to prepare
What Is a CSI Mini Mystery Detective?
A CSI Mini Mystery Detective is a single printed case your class cracks with math. The lineup of suspects each carry a number, the questions produce those numbers, and every correct answer takes one suspect out until a single name is left holding it. The arithmetic is the whole puzzle, so there is no kit and nothing to charge, and that is what makes detective activities land differently from a page of math worksheets. One case fits one class period.
When to Use This Resource
This is the practice day after you teach three digit regrouping, and the start of year check when you want to know whether last year's class kept it. Double regrouping is where most of the class comes unstuck, and a plain worksheet lets a wrong hundreds column go by unnoticed. Here it strikes off the wrong suspect, so the student finds it and fixes it before the page reaches you.
Use it for test prep, homework, math centers, morning work, early finishers, sub plans and homeschool lessons, with a whole class, a small group or a single student.
Grade Levels
Written for 3rd grade, where three digit regrouping sits in the standards, and used with 4th and 5th graders as a start of year check. Second graders take it once two digit regrouping is secure and they are ready for the next column.
Why Teachers Love These Cases
- Regrouping twice in a sum, which is the part students skip
- Students correct themselves when the wrong name comes off the lineup
- No prep, and the answer keys make grading quick
- Works with a whole class, a small group, partners, or one student alone
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