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Adding Fractions with Like Denominators

A 50-minute Grade 4 lesson on adding and subtracting fractions that share a denominator, built on the idea that 3/5 is simply three of the thing called a fifth.

Adding Fractions with Like Denominators is a free 50-minute Grade 4 maths lesson plan for Common Core standard 4.NF.B.3 — add and subtract fractions with the same denominator. It is timed across 5 sections, gives the exact wording to use where the wording carries the mathematics, names 3 misconceptions with the teaching move that addresses each, and ends with an exit ticket and a printable worksheet with its answer key.

Grade:
Grade 4
Length:
50 minutes
Standard:
4.NF.B.3

Grade 4 · Number & Operations — Fractions

4.NF.B.3

Understand a fraction a/b with a > 1 as a sum of fractions 1/b; add and subtract fractions with like denominators.

Objective

Students will be able to add and subtract fractions with like denominators and decompose a fraction into a sum of unit fractions.

Students are successful when they can

  • Adds fractions with the same denominator without changing the denominator.
  • Writes 5/8 as a sum of unit fractions.
  • Adds mixed numbers with like denominators.

What you need

  • Fraction strips and circles
  • Number lines marked in eighths and fifths
  • Fraction cards
  • The printable practice sheet linked at the end of this plan

The lesson

Warm-up — count in fifths

6 min
  1. Count aloud: one fifth, two fifths, three fifths, four fifths, five fifths, six fifths.
  2. Ask what five fifths is. One whole, and the count carries straight past it.

Teach — counting the same thing

15 min
  1. Write 2/5 + 1/5. Build both with strips. Two fifths and one more fifth is three fifths.
  2. Ask why the denominator did not change. Because you were counting fifths and you are still counting fifths.
  3. Compare with 2 apples plus 1 apple. Nobody writes 3 apples-squared, and nobody adds the denominators either.
  4. Decompose: 5/8 is 1/8 + 1/8 + 1/8 + 1/8 + 1/8, and also 3/8 + 2/8. Both are true.
  5. Subtract: 7/8 − 3/8 is four eighths left, and the strips show it.
  6. Finish with mixed numbers: 2 1/4 + 1 2/4. Add the wholes, add the quarters, and check whether the quarters make another whole.
“Three fifths is three of something called a fifth. Add two more of them and you have five of them. The name of what you are counting does not change.”

Guided practice — build then write

14 min
  1. Pairs build each addition with fraction strips before writing it.
  2. They decompose one fraction into unit fractions two different ways.
  3. Then they add two mixed numbers, checking whether the fraction part exceeds a whole.

Independent practice

12 min
  1. Students complete an adding fractions page.
  2. Added denominators are the diagnostic error and are usually consistent across the page rather than occasional.

Close

3 min
  1. Give 4/6 + 3/6 and ask what the answer means.
  2. Seven sixths, which is more than one whole, and that is allowed.

What goes wrong, and why

Each of these is a reasoning error rather than carelessness. The fix addresses the reasoning.

Adds 2/5 + 1/5 as 3/10.

Why: Both numbers have been treated as separate quantities to add, which is what the notation looks like. Nothing in the symbols says the denominator is a unit name.

Fix: Build it with strips. Three tenths is visibly smaller than two fifths, so the answer cannot be right, and the pupil sees why.

Writes 7/5 as an error and tries to reduce it to 1 or 2.

Why: A numerator larger than the denominator still reads as impossible, left over from fractions being parts of one shape.

Fix: Count in fifths past the whole on a number line. Seven fifths has a position and there is nothing wrong with it.

Adds mixed numbers by adding wholes and fractions separately and leaving 3 6/4.

Why: The two parts have been added correctly and the check on whether the fraction part exceeds one has not been made.

Fix: Ask how many quarters are in a whole. Six quarters is one whole and two quarters, so the answer is 4 2/4.

If they are not there yet

  • Work with strips for every calculation and with denominators of 2, 4 and 8 where the pieces are familiar.
  • Say the unit aloud — 'two fifths plus one fifth' — before writing anything.

If they finish early

  • Subtract a fraction from a whole number: 3 − 2/5.
  • Decompose a mixed number into unit fractions.
  • Solve a word problem needing two fraction additions.

Exit ticket

Work out 3/8 + 4/8 and 2 3/5 + 1 4/5. Then write 5/6 as a sum of unit fractions.

What to look for: 7/8, 4 2/5, and 1/6 five times. An answer of 7/16 to the first is the added-denominator error; 3 7/5 means the extra whole was not converted.

Printable practice for 4.NF.B.3

Free to print and copy, answer key included. Each sheet can generate a fresh set of problems for a retake.

Questions about Adding Fractions with Like Denominators

How long does the Adding Fractions with Like Denominators lesson take?

50 minutes, split across 5 timed sections: warm-up 6 min, teach 15 min, guided practice 14 min, independent practice 12 min, close 3 min. The minutes are stated per section and add up to the stated length, so the plan can be cut or extended at a section boundary rather than abandoned halfway.

Which standard does Adding Fractions with Like Denominators teach?

CCSS.MATH.CONTENT.4.NF.B.3 — 4.NF.B.3, Number & Operations — Fractions for Grade 4: “Understand a fraction a/b with a > 1 as a sum of fractions 1/b; add and subtract fractions with like denominators.” In plain terms, add and subtract fractions with the same denominator.

What do I need to teach this lesson?

Fraction strips and circles, number lines marked in eighths and fifths, fraction cards and the printable practice sheet linked at the end of this plan. Everything listed is either ordinary classroom equipment or a free printable from this site — there is nothing to buy and nothing to prepare beyond photocopying.

What mistakes should I expect in this lesson?

Three, each a reasoning error rather than carelessness: adds 2/5 + 1/5 as 3/10; writes 7/5 as an error and tries to reduce it to 1 or 2 and adds mixed numbers by adding wholes and fractions separately and leaving 3 6/4. The plan gives the thinking behind each one and the teaching move that addresses the thinking rather than the symptom.

How do I know whether the lesson worked?

The exit ticket asks: “Work out 3/8 + 4/8 and 2 3/5 + 1 4/5. Then write 5/6 as a sum of unit fractions.” 7/8, 4 2/5, and 1/6 five times. An answer of 7/16 to the first is the added-denominator error; 3 7/5 means the extra whole was not converted. That tells you whether the class needs a reteach or a thirty-second conversation before you plan tomorrow.

Is there a worksheet to go with Adding Fractions with Like Denominators?

Yes — 2 printable 4.NF.B.3 worksheets, linked at the end of the plan and free like the rest of the site. Each one comes with an answer key and 25 versions, so the practice after the lesson can be a different paper on every desk.

Is Adding Fractions with Like Denominators free to use?

Yes. The plan, its printables and their answer keys are free to read, print and photocopy for your own class, with no account and no email capture. It was last reviewed on 5 September 2026. Please do not resell it or republish it as your own.

Last reviewed 2026-09-05. Aligned to 4.NF.B.3 of the Common Core State Standards for mathematics.