Lesson Plan
Decimal Detectives Lesson Plan
Students will learn to read, write, and compare decimal numbers to the thousandths place through a detective-themed investigation, reinforcing place value understanding and problem-solving skills.
Mastering decimal place value is essential for future math topics (operations, measurement, financial literacy). This engaging, real-world approach builds confidence, accuracy, and motivation to tackle decimals.
Audience
5th Grade Students
Time
30 minutes
Approach
Thematic hands-on activities to reinforce decimal place value.
Materials
- Decimal Detectives Slide Deck, - Decimal Case Files Worksheet, - Place Value Investigation Cards, - Investigation Report Template, - Whiteboard and Markers, and - Student Math Notebooks
Prep
Teacher Preparation
10 minutes
- Review the Decimal Detectives Slide Deck
- Print enough copies of the Decimal Case Files Worksheet for all students
- Cut out the Place Value Investigation Cards
- Prepare copies of the Investigation Report Template
- Set up whiteboard space and gather markers
Step 1
Introduction
5 minutes
- Display the Decimal Detectives Slide Deck cover slide and theme
- Explain that students are decimal detectives solving place-value mysteries
- Quick group review: reading and writing decimals to thousandths
- Pose a “mystery number” and solve together on the board
Step 2
Guided Practice
10 minutes
- Hand out the Decimal Case Files Worksheet
- Model solving two sample case-clues on the whiteboard
- Students work in pairs to complete the first two clues
- Discuss as a class the strategies used for each decimal
Step 3
Detective Activity
10 minutes
- Distribute Place Value Investigation Cards to each pair
- Students rotate through three stations, uncovering decimal puzzles
- At each station, record findings on the Investigation Report Template
- Teacher circulates to provide support and check understanding
Step 4
Wrap-Up and Reflection
5 minutes
- Reconvene and invite pairs to share one interesting decimal discovery
- Compare how different strategies helped decide which decimals were larger or smaller
- Collect worksheets and investigation reports
- Preview the next lesson: adding and subtracting decimals
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Slide Deck
Decimal Detectives
Welcome, 5th Grade Decimal Detectives!
Today we'll solve decimal mysteries together.
Welcome students to the Decimal Detectives theme. Show excitement—wear your detective hats! Explain that today we’ll solve decimal mysteries together. Point out that mastering decimals will help with future math and real-world tasks.
Learning Objectives
- Read and write decimals to the thousandths place
- Compare and order decimals using place value
Read each objective aloud. Emphasize that by the end, they’ll be able to read/write decimals to thousandths and compare their sizes accurately. Connect to why detectives need precision.
Place Value Review
Decimal Places:
- Tenths (0._ _)
- Hundredths (0._ _)
- Thousandths (0._ _ _)
Example: 3.142 = 3 ones, 1 tenth, 4 hundredths, 2 thousandths
Use the whiteboard to draw a place-value chart. Have students chime in the names of each place as you point. Reinforce what each decimal place represents.
Guided Practice
Solve these mystery numbers together:
- Read and write 0.307
- Identify the value of the digit 5 in 4.569
Model thinking aloud as you read 0.307 (“zero point three zero seven: three hundred seven thousandths”). Then show how to identify the digit value in 4.569. Invite volunteers to come up.
Detective Activity
In pairs:
- Use the Decimal Case Files worksheets
- Rotate through 3 stations with decimal puzzles
- Record your findings on the Investigation Report Template
- I'll circulate to help!
Explain materials: hand out the Decimal Case Files Worksheet, Place Value Investigation Cards, and Investigation Report Template. Remind pairs to rotate through each station and record findings as detectives.
Station Map
Station 1: Missing Decimal – Find the hidden number
Station 2: Decimal Ordering – Arrange from smallest to largest
Station 3: Place Value Puzzle – Build decimals on grid
Briefly describe each station. Allocate ~3 minutes per station and give a 30-second warning before rotating. Ensure smooth transitions.
Wrap-Up & Reflection
Share one interesting discovery:
- What strategy helped you compare decimals?
- Which decimal mystery surprised you?
Invite pairs to share one strategy that helped them compare decimals or an interesting discovery. Collect their reports and preview next lesson on adding/subtracting decimals.
Worksheet
Decimal Case Files Worksheet
Detective, welcome to your first mission! Use your decimal skills to crack each case. Show your work and write your answers in the spaces provided.
Case File #1: The Missing Thousandths
A suspect’s code is 0.5_7. The underscore (_) hides the thousandths digit. Find the missing digit to complete the code.
Missing digit: _______
Case File #2: Suspect Identification
Read the decimal 0.384 as words for your report (e.g., “zero point three eight four”).
Written in words: ______________________________________________________
Case File #3: Place Value Stakeout
The getaway car’s license plate reads 3.207. Identify the digit in the hundredths place and explain its value.
Digit in hundredths place: _______
Value of that digit: ____________________________________________________
Case File #4: Decimal Dossier
Arrange these suspect IDs from smallest to largest:
• 0.245 • 0.254 • 0.24
Order (smallest → largest):
Case File #5: Undercover Operation
Create a secret decimal that has exactly 2 tenths, 3 hundredths, and 5 thousandths.
Your decimal: _______
Case File #6: Code Breaker
Translate “seven thousandths” into decimal form for your final clue.
Decimal form: _______
Detective, record all your findings on the Investigation Report Template and prepare to share your evidence!
Activity
Place Value Investigation Cards
Station 1: Missing Decimal
Fill in the missing digit for each code.
- 0._56 (blank is the tenths place; code equals 456 thousandths)
Answer: _______ - 0.7_9 (blank is the hundredths place; code equals 709 thousandths)
Answer: _______ - 0.32_ (blank is the thousandths place; code equals 0.329)
Answer: _______
Station 2: Decimal Ordering
Arrange these decimal codes from smallest to largest.
• 0.2
• 0.256
• 0.26
• 0.265
Order (smallest → largest):
- ________ 2. ________ 3. ________ 4. ________
Station 3: Value Matching
Write or identify the decimal based on place-value clues.
a) Write the decimal for “3 ones, 4 tenths, and 5 thousandths”: _______
b) In the decimal 6.507, what is the value of the digit 5? _______
c) Write the decimal described by “zero ones, three tenths, zero hundredths, eight thousandths”: _______
Place these cards at your stations. Students record answers on the Investigation Report Template as they rotate.
Worksheet
Investigation Report Template
Detective, record your findings for each station below. Be precise and clear in your evidence.
Station 1: Missing Decimal
List each code and the missing digit you found.
- Code: 0._56 → Missing digit: _______
- Code: 0.7_9 → Missing digit: _______
- Code: 0.32_ → Missing digit: _______
Station 2: Decimal Ordering
Write the decimals in order from smallest to largest.
- ________
- ________
- ________
- ________
Station 3: Value Matching
Answer each place-value clue.
a. Write the decimal for “3 ones, 4 tenths, and 5 thousandths”: _______
b. In the decimal 6.507, what is the value of the digit 5? _______
c. Write the decimal for “zero ones, three tenths, zero hundredths, eight thousandths”: _______
Reflection and Strategy
- Which strategy helped you most when comparing or ordering decimals? Why?
- What was your most interesting decimal discovery today?
Detective, be prepared to share your evidence and strategies with the class! Use this report to support your explanation.