Addition and Subtraction Within 20
Mystery Detective · Grades 1–2
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Inside the case file
A sub folder, a math center and an early finisher task in one file: a CSI Mystery Detective math case that runs as SCOOT task cards around the room, on addition and subtraction within 20 for 1st grade. Written to 1.OA.C.6, so students add and subtract on the question cards, then strike a suspect off the sheet until one name is left, which gives you math worksheets and math activities from one no prep download. Nothing in it is seasonal, so it runs from back to school in August through to the end of year. Color and black and white versions, with a full answer key and detective activities that get your class moving.
Students will happily do a whole session of math facts if they are on their feet and there is a culprit at the end of it. The cards go up around the room, each answer takes a suspect off the sheet, and the class works its way round. Cut them once and you have an activity for every year after this one, ready for early finishers too.
The Mischievous Magician
The magician is up to something and the class has been called in. Students move from card to card, and each answer they solve rules out another suspect on the sheet they carry. The last name left when every card is done is the one behind it all.
What's Inside
- Eleven numbered question cards to put up around the room
- Addition and subtraction within 20, written to 1.OA.C.6
- A suspect sheet each student carries and crosses names off as they go
- A color set and a black and white set of the same cards
- The answer key, with the culprit named
- Print, cut the cards once, and the set is ready for good
What Is a CSI Mystery Detective?
A CSI Mystery Detective gives your class a crime, a lineup and a set of questions, and the only route to the culprit runs through the math. Each suspect wears a number, each correct answer matches one of them, and that name is struck off until a single suspect has not been ruled out. Run as SCOOT the questions go on the wall and students travel between them, which is what separates detective activities from a page of math worksheets. One case fills a class period.
When to Use This Resource
Reach for this when the facts within 20 need another run and nobody will sit through a third worksheet. Sending students around the room turns the same eleven questions into a lesson they finish, and the suspect sheet makes each one matter because a wrong sum takes out the wrong person. It is also the folder to leave behind when you are out for the day.
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 one child alone.
Grade Levels
Written for 1st grade, where 1.OA.C.6 sits in the standards. Kindergarten classes take it late in the year once addition within 10 is secure, and second graders use it as a start of year warm up before moving on to within 100.
Why Teachers Love These Cases
- Students are up and moving, which keeps first graders working
- The suspect sheet flushes out a wrong answer without you checking it
- One cut and the cards last for years
- Works with a whole class, a small group, partners, or one student alone
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