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"Great resource, low prep, easy to use, and fun! Thank you for sharing this! Highly recommend to other teachers!"

Brandie K.

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"My students loved this resource! They were engaged and were able to complete the tasks with ease."

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"I have enjoyed every purchase I've made from your store. The students are always so engaged!"

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Kiwiland Education

Halloween Addition & Subtraction Within 100 CSI Mystery Worksheets | Grades 1–3 | The Haunted House

$4.50 USD

October Halloween CSI math worksheets on addition and subtraction within 100, built as a CSI Mystery Detective case about the house on the corner that everybody has a story about. Pitched at 2nd grade and 3rd grade, it gives the class a subtraction mystery with an actual monster at the end, and it prints in color or black and white with nothing to prepare. This week somebody actually went inside and came back out with a description that matches nothing anyone has heard before. Answer keys are included. Students check worked answers for errors, color the correct arrow and follow linked clues to the monster's final age, crossing off a suspect with each correct answer.

The Case: Who Haunts The House?

You do not really believe the stories your friends tell about demons and hauntings, but they are good stories, and the best of them is always about the house on the corner. Everyone knows the one. This week somebody actually went in, and came back out again with a description that does not match anything anybody has heard before.

What's Inside

  • Checking worked answers for errors and tallying which are correct
  • Addition within 100 across the clue pages
  • Addition problems used to color the correct arrow to the next problem
  • Two-digit subtraction used to settle a clue about the monster
  • A sequence of linked clues that builds to the monster's final age
  • Full color and black-and-white versions of every page
  • Answer keys for the whole case

What Is a CSI Mystery Detective Case?

The premise of a CSI Mystery Detective case is that the math breaks the alibis. Students solve, each correct answer removes one suspect from the line-up, and the last name standing is the one who did it. It is a math escape room with no locks, no app and nothing to set up. Detective activities are harder to coast through than ordinary math worksheets, because the deduction only closes on correct work. It fills a whole math activity, suits math centers, and works as a sub plan.

When to Use This Resource

  • Halloween week in October, when a normal worksheet will not hold them
  • Addition and subtraction within 100 review before or after a unit test
  • Math centers, early finishers and independent work
  • Emergency sub plans that run themselves
  • End of year review, when attention is thin and the work still has to happen

Grade Levels

Built for 2nd grade and 3rd grade. Second graders run it comfortably, which makes it a good one for a class that needs a win; third graders finish inside a lesson. It also suits 1st grade students who are ahead and ready for two-digit work with something at stake.

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 Halloween activity that still does real math
  • Works as a whole lesson, a center, or a filler for an awkward afternoon

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  • Thank you from Kiwiland Education

"Great resource, low prep, easy to use, and fun! Thank you for sharing this! Highly recommend to other teachers!"

Brandie K.

Verified buyer

"My students loved this resource! They were engaged and were able to complete the tasks with ease."

Gina H.

Verified buyer

"I have enjoyed every purchase I've made from your store. The students are always so engaged!"

Karen C.

Verified buyer

How CSI Math Mysteries Work

CSI Math Mysteries turn regular math practice into a clue-based investigation. Students solve problems, use their answers as evidence, and eliminate suspects until the case is solved.

1

Read the Case

Students begin with a short mystery scenario and find out what needs to be solved.

2

Solve the Clues

Each clue gives students focused math practice using the target skill for that resource.

3

Eliminate Suspects

Students use their answers to remove suspects from the investigation one clue at a time.

4

Crack the Case

By the end, only one suspect remains and students can reveal the answer to the mystery.

No apps, locks, passwords, or student logins are required. Just print and go.

New to the format? Read What Is a Math Mystery? for how they work and how to run one in class.

Why Teachers Use CSI Math Mysteries

CSI Math Mysteries turn skill practice into a clue-based investigation students want to solve. They are easy to prep, flexible for different classroom routines, and help students practice math skills while using logic, reasoning, and careful problem solving.

Teacher-Friendly Review

Practice that feels like a mystery, not another worksheet.

CSI Math Mysteries help students stay focused by turning skill practice into a clue-based case. They are easy to prep, simple to use, and flexible enough for busy classroom routines.

No-Prep and Print-and-Go

Use the pages right away for review, math centers, sub plans, small groups, early finishers, or homeschool math.

Encourages Careful Thinking

Students need accurate answers to eliminate suspects, which encourages checking, reasoning, and attention to detail.

Easy to Fit Into Lessons

Use a full mystery in one session or split the clues across centers, partner work, intervention, or review rotations.

Builds Student Confidence

The mystery format gives students a clear purpose for practicing math skills and helps make review feel more rewarding.

CSI Math Mysteries combine focused math practice with problem solving, logic, and a detective-style task that students can complete independently or with support.

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Frequently Asked Questions For CSI Math Mysteries

Printable CSI Math Mystery worksheets that turn math practice into clue-based detective investigations.

Is this CSI Math Mystery a digital activity?

No. This is a printable PDF resource. Students complete the CSI Math Mystery on paper. No physical item will be shipped.

Do students need apps, locks, passwords, or logins?

No. Students do not need apps, locks, passwords, or logins. Teachers can print the pages and use the CSI Math Mystery straight away.

How do students solve the CSI Math Mystery?

Students solve math clues and use their answers to eliminate suspects. Each correct answer helps them narrow down the case until only one suspect remains.

Can this CSI Math Mystery be used for sub plans?

Yes. CSI Math Mysteries work well for sub plans because students can work through the clues independently, with a partner, or in small groups.

Can this CSI Math Mystery be used for homeschool?

Yes. This printable CSI Math Mystery can be used for homeschool lessons, tutoring, review practice, enrichment, or extra math support.

Will this work for early finishers or math centers?

Yes. CSI Math Mysteries are a good fit for early finishers, math centers, small groups, independent work, review lessons, and extra practice activities.

Haunted house halloween mystery detective add subtract within 100

Halloween Addition & Subtraction Within 100 CSI Mystery Worksheets | Grades 1–3 | The Haunted House

$4.50

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