100th Day of School Missing Numbers to 100 Mystery Detective Activity

100th day of school math worksheets for 1st grade and 2nd grade: five cases of missing numbers to 100, where the number before and the number after is what crosses a place or a number off the clue list. The 100 day treats have gone, a hundred stickers are nowhere in sight and a hundred gremlins are loose in the school, so counting to 100 is the only way through, and a wrong number matches no clue. Print and go with full answer keys: no prep CSI Mini Mystery Detective math cases for morning work, math centers, early finishers, homework and sub plans.

The 100th day of school lands in late January in most rooms, and it needs something the class will sit down and do between the crown-making and the counting collections. A six year old will write the number before and after all morning to find out where the chocolates went, and one case fits a morning work slot. Five math cases in one Mystery Detective download covers the week around it.

The Cases

1. Missing Chocolates - the 100 day treats have gone
2. Missing Number to 100 - one number is off the chart
3. Missing Stickers - a hundred stickers, none in sight
4. 100 Hidden Gremlins - gremlins loose in the school
5. Principals Birthday - nobody knows their age

What's Inside

• Five case files on the number before and the number after to 100
• Twelve questions a page: three cases on the number after, two on the number before
• One case works in number words, so reading numbers gets practiced as well
• A dozen clues down the side, crossed off one answer at a time
• A red-ink answer key for all five cases, and a certificate page for a closed case
• Print and go: no cutting, no laminating, nothing to prepare

What Is a CSI Mini Mystery Detective?

A CSI Mini Mystery Detective is one printed page with a crime at the top and a list of clues beside the questions. Each clue carries a number, the answers on the page produce those numbers, and a match strikes that clue out. The one clue nobody matched is the solution. Nothing is cut, laminated or charged, and counting correctly is the only way through.

When to Use This Resource

The obvious week is the 100th day itself, in late January or early February, and the days either side when the room is full of hundred-themed everything. It works as ordinary number sense practice at any point, because the child is counting on and counting back inside a hundred. All the instructions are on the page, so it goes into a sub folder as it is.

Use it for morning work, math centers, early finishers, homework, sub plans and homeschool lessons, with a whole class, a small group or one student.

Grade Levels

Written for 1st grade, where writing numbers to 100 sits in the standards. Second graders use it as a start of year check, and kindergarten classes late in the year once they are confident past fifty.

Why Teachers Love These Cases

• A miscount matches no clue, so a child spots it without being told
• Nothing to prepare on a day that is already busy
• Five short cases covers the hundredth-day week
• Works with a whole class, a small group, partners or one student

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