Adding Decimals: Line up the Points

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1 Getting Started
2 Watch and Notice
3 Try It Together
4 Line up the Points in Your Copy
5 Class Challenge
6 What Did We Notice?
7 What's Next
Pupil practice

1 - Getting Started ~3 mins

Look at the sum on the board. Someone has stacked the two numbers using the right edge of the digits — the 7 sits directly above the 5:

   4.7
+ 0.85
  -----

Watch out

Notice that the decimal point in 4.7 does not sit directly above the decimal point in 0.85. They wander.

Hands up: what is wrong with how these two numbers have been lined up?

Teacher Notes

The wrongly-aligned sum is now on the IWB as part of the description — you don't need to redraw it. Take three hands-up answers, not open call-outs; you are listening for someone to say the decimal points are not in a single vertical line, or that the 7 (tenths) is sitting over the 8 (tenths) but the 5 (hundredths) has nothing above it. Don't tell them the rule yet — let the next step do the teaching.

If pupils only say 'it looks wrong' without naming why, revoice: 'so where exactly is the problem? Point at the part that is wrong.' The goal of this hook is curiosity, not the answer.

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watch and Notice ~9 mins

Now watch four worked sums on the column-addition interactive. The decimal points line up in a single vertical line every time. Where one number we're adding has fewer places, a zero holds the empty column. Notice how the carry-1 jumps the same way it did with whole numbers.

Example 1: 4.7 + 0.85 = 5.55

The trailing-zero trick: 4.7 becomes 4.70 so the hundredths column has something to add.

Example 2: 0.3 + 0.27 = 0.57

Same idea on smaller numbers: 0.3 becomes 0.30.

Example 3: 1.05 + 2.345 = 3.395

The lonely thousandth: 1.05 becomes 1.050 so the thousandths column has a 0 above the 5.

Example 4: 9.99 + 0.01 = 10.00

The cascade regroup: every column tips over a 10, the carry-1 ripples all the way to the units, and the answer crosses one whole.

Teacher Notes

Walk each example aloud, one at a time. On each one, pause and ask the class 'where does the decimal point go?' before the answer lands. Break up the four-example beat with the pacing cues below so the watch does not turn into one long block.

Example 1 — 4.7 + 0.85. Emphasise rewriting 4.7 as 4.70. The zero isn't extra, it's holding the hundredths column open.
Example 2 — 0.3 + 0.27. Same trick, smaller numbers. Quick. Pacing lever: after this one, ask the class to read the rule back to you: 'line up the points, fill the empty columns with zeros, then add.'
Example 3 — 1.05 + 2.345. Pacing lever: before revealing the answer, turn to one pupil and ask 'what holds the thousandths place in 1.05?' — they name a zero, then you reveal. Point at the lonely 5 in the thousandths column of 2.345 as you do.
Example 4 — 9.99 + 0.01. Slow down. Let the cascade ripple visibly across the screen: hundredths 0 carry, tenths 0 carry, units land at 10. The answer is 10.00, not 10 — the trailing zeros matter for precision.

Do not move on until the class can name the rule out loud: 'line up the decimal points, fill the empty columns with zeros, then add.'

👇 Mark your steps as done as you complete them.

+10 XP

3 - Try It Together ~13 mins

Today we work two sums together on the IWB.

First: 6.4 + 2.85. Where does the decimal point go in the answer before any digit lands? Where does the trailing zero need to sit on 6.4?
Then: 0.7 + 0.567. This one has two empty places to fill on 0.7, and the answer crosses one whole.

Tip

Pupils take turns at the board. The class agrees or corrects out loud.

6.4 + 2.85

Teacher Notes

This round is for talking it through together — pupils take turns at the board and the class agrees or corrects out loud.

Open the interactive on 6.4 + 2.85. Walk through column-by-column: hundredths first (0 + 5 = 5), tenths next (4 + 8 = 12, write 2, carry 1), units (6 + 2 + carry 1 = 9). Sum is 9.25. Have one pupil drive each column from the board.

Then run the second problem with the class: 0.7 + 0.567. The trailing-zero trick lives in two places here (0.7 → 0.700), and the answer is 1.267 — crosses one whole. Ask 'where did the carry come from?' on the unit column.

If a pupil at the board lines digits up by the right edge, do not just correct — ask the class 'what's missing?' and let another pupil revoice the points-line-up rule.

+15 XP

4 - Line up the Points in Your Copy ~5 mins

COPYBOOK MOMENT

Illustration for Line Up the Points in Your Copy In your maths copy, set up these three decimal sums vertically — one under the other — with the decimal points lined up in a single straight line down the page. Fill any empty column with a zero before you add.

4.7 + 0.85
1.05 + 2.345
9.99 + 0.01

We will work each column together, and you write the answer with the decimal point in the right place.

Teacher Notes

Whole-class copybook practice — every pupil writes together, IWB paused. Allow about a minute for set-up (vertical alignment of points only, no adding yet), then work each sum column-by-column with the class, pausing after every column for pupils to write the digit and any carry in their own copies before the next column starts.

Walk the room glancing for the vertical alignment of decimal points — this is whole-class copybook practice, not marking. The most common error is right-edge alignment (digits flush right, points crooked). Tap the desk of any pupil whose points wander; do not say the rule for them. Watch for missing trailing zeros — if a pupil has 4.7 over 0.85 with the hundredths column empty above the 5, ask quietly 'what holds that column?'

On 9.99 + 0.01, slow the pace deliberately — narrate the cascade as the class writes: 'hundredths make 10, write 0 carry 1; tenths now make 10, write 0 carry 1; units make 10, write 0 carry 1 — answer is 10.00.'

+10 XP

5 - Class Challenge ~12 mins

Today's bank: five decimal sums that get harder as we go. The first two should be quick.

Watch out

One of these has a surprise carry — watch for it.

Decimal addition: practice bank

Teacher Notes

This round is the practice bank — pupils take turns at the board, check each answer, and the class confirms before moving on. The same 5-problem bank reruns at home as tonight's homework, so keep the board work brisk rather than over-explaining.

Send a different pupil to the board for each problem. Before they tap Check, ask the class to predict the unit digit of the answer — this catches lazy carrying. Watch especially for:

Problem 3 (3.6 + 1.85): the carry from hundredths to tenths.
Problem 4 (2.07 + 1.953): three decimal places vs. two — does the trailing zero appear?
Problem 5 (6.99 + 0.01): the cascade — pause on this one, let the carry ripple visibly, and check the answer reads 7.00 not 7.

If a pupil's check fails, ask 'which column went wrong?' — do not show them; let them re-walk the sum on the board.

+15 XP

Pupil practice

Module 2 · Operations and Computational Fluency Number

Lesson 19 · Adding Decimals: Line up the Points

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Teacher Class Feed

1 - Getting Started ~3 mins

2 - Watch and Notice ~9 mins

Example 1: 4.7 + 0.85 = 5.55

Example 2: 0.3 + 0.27 = 0.57

Example 3: 1.05 + 2.345 = 3.395

Example 4: 9.99 + 0.01 = 10.00

3 - Try It Together ~13 mins

6.4 + 2.85

4 - Line up the Points in Your Copy ~5 mins

5 - Class Challenge ~12 mins

Decimal addition: practice bank

Unlock the full learning experience

XP