Missing Numbers to 120
Back to School Mystery · Grades 1–2 · Detective Mystery
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Inside the case file
Missing numbers to 120 worksheets for 1st grade: three CSI Mini Mystery Detective math cases where students write the number before and after, then cross a suspect off the lineup until the culprit is left. One case runs to 100 and two to 120, so counting practice is built in from the first week back, and every answer matches one suspect only. Back to school math activities for August and September, then morning work, math centers, early finishers and sub plans whenever number order slips.
The first week of first grade is for finding out who can count past a ten without the chart on the wall, and this does it without anything that looks like a test. Students fill the gaps, match the numbers to a suspect and cross the name off, so they keep going for the culprit. Three CSI Mini Mystery Detective math cases, three mornings, answer keys included.
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
- Missing numbers before and after, to 100 on one case and to 120 on the others
- Number sequences printed with gaps for students to fill in
- 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 hands your class a crime and a lineup and asks them to solve it with math. Work the crime sheet, match each answer to the suspect carrying that number, cross the name off, and keep going until one suspect has not been ruled out. Because the elimination only works when the numbers are right, these detective activities make students check themselves in a way math worksheets rarely do. One case takes about a class period, with nothing to prepare.
When to Use This Resource
August and September is where this belongs, in the first weeks back when the counting sequence has gone soft over the summer and you need to see who has kept it. The set tells you that quickly, because a student who cannot go past 109 will cross off the wrong suspect and know it straight away. It is a check on the skill that does not feel like a test to the child sitting it.
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 student alone.
Grade Levels
Written for 1st grade, where counting to 120 sits in the standards, and used with 2nd graders as a start of year check. Kindergarten classes take the case that stops at 100 once they are confident past fifty.
Why Teachers Love These Cases
- Shows you fast which students lose the sequence at the tens
- Students find their own mistakes as the suspects come off
- No prep in the busiest weeks of the year
- Works with a whole class, a small group, partners, or one student alone
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