Here is a classroom-ready 15-minute lesson designed to pair directly with the Math-aids Adding and Subtracting Decimals.

15-Minute Math Lesson Plan: Adding and Subtracting Decimals

Grade Level: 4–6
Time: 15 minutes
Topic: Adding and Subtracting Decimals to the Hundredths Place

Learning Objective

Students will add and subtract decimal numbers accurately by lining up decimal points, calculating by place value, and regrouping when necessary.

Materials

• Math-aids Mixed Decimals worksheet

• Pencil

• Whiteboard or projector

1. Warm-Up — 3 Minutes

Write these two problems on the board:

Problem A: 12.34 + 5.21

Problem B: 18.75 − 6.32

Ask students:

• What do you notice about the decimal points?

• Why should the decimal points line up?

Explain that digits must be lined up by place value: ones under ones, tenths under tenths, and hundredths under hundredths.

Answers:

• 12.34 + 5.21 = 17.55

• 18.75 − 6.32 = 12.43

2. Teacher Modeling — 4 Minutes

Use two actual problems from the worksheet.

Example 1: Addition With Regrouping

Worksheet problem: 45.93 + 82.92

Write the numbers vertically, lining up the decimal points.

   45.93
+  82.92
--------
  128.85

Explain the steps:

1. Hundredths: 3 + 2 = 5.

2. Tenths: 9 + 9 = 18 tenths. Write 8 tenths and regroup 1 whole.

3. Ones: 5 + 2 + 1 = 8.

4. Tens: 4 + 8 = 12.

Answer: 128.85

Example 2: Subtraction With Regrouping

Worksheet problem: 68.49 − 44.47

   68.49
-  44.47
--------
   24.02

Explain:

1. Hundredths: 9 − 7 = 2.

2. Tenths: 4 − 4 = 0.

3. Ones: 8 − 4 = 4.

4. Tens: 6 − 4 = 2.

Answer: 24.02

Remind students that the decimal point stays aligned throughout the calculation.

3. Guided Practice — 3 Minutes

Solve these actual worksheet problems together.

Problem 1: Subtraction

67.15 − 41.36

The hundredths and tenths require regrouping.

Answer: 25.79

Problem 2: Addition

34.62 + 12.14

Add each place value:

Answer: 46.76

Problem 3: Subtraction

34.87 − 18.86

Subtract each place value:

Answer: 16.01

Ask students:

“What is the first thing you should do before adding or subtracting decimals?”

Expected response: Line up the decimal points.

4. Worksheet Practice — 3 Minutes

Have students work independently on the attached worksheet. It contains 20 addition and subtraction problems involving decimal numbers to the hundredths place. <FileCite ref_id="turn2file0" />

Encourage students to use this routine:

1. Line up the decimal points.

2. Add zeros if needed to make the place values easier to compare.

3. Add or subtract from right to left.

4. Regroup when necessary.

5. Bring the decimal point straight down into the answer.

6. Estimate to check whether the answer makes sense.

As students work, look for correctly aligned decimal points and accurate regrouping.

5. Exit Ticket — 2 Minutes

Use this actual worksheet problem:

56.58 − 55.65

Ask students to solve independently.

   56.58
-  55.65
--------
    0.93

Answer: 0.93

Ask: “Why is the answer less than 1?”

Expected response: The difference is 93 hundredths, which is less than one whole.

Differentiation

Students needing support:

• Use graph paper to line up digits by place value.

• Start with problems that do not require regrouping.

• Allow students to label the ones, tenths, and hundredths columns.

Students working at grade level:

• Complete a mix of addition and subtraction problems.

• Show each step and check answers with estimation.

Students needing a challenge:

• Focus on problems with multiple regrouping steps.

• Solve problems with answers greater than 100.

• Explain how estimation can reveal an unreasonable answer.

Common Misconceptions

• Misaligning decimal points: Always line up the decimal points, not the last digits.

• Forgetting to regroup: Regroup when a column total is 10 or more, or when a subtraction digit is too small.

• Dropping the decimal point: The decimal point must appear in the answer directly below the aligned decimal points.

• Ignoring place value: 0.9 and 0.09 have different values.

Assessment

Students demonstrate understanding when they can:

• Align decimal points correctly.

• Add and subtract hundredths.

• Regroup accurately.

• Place the decimal point correctly in the answer.

• Check their work using estimation.

Success Criteria

“I can add and subtract decimals by lining up decimal points, using place value, and regrouping when needed.”

Teacher tip: Since this worksheet mixes addition and subtraction, have students identify the operation sign before beginning each problem. This simple habit helps prevent calculation errors.

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Posted 10/15/26

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