Logic Masters · Ages 11 to 12
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Logic Masters · Ages 11 to 12
All Logic Masters gamesDecimal Column Add Lab
Line the decimal points up, then add or subtract. For ages 11 to 12.
SimulationDecimal column addition: line up the points~10 min per level5 levelsAll devices
- Free · no account required
- COPPA compliant
- +10 XP per level
- 5 levels
- Plays on all devices
- Curriculum-aligned
The learning journey
Every activity is one step. Here is where this one fits.
- Play(you are here)Learn the idea in a game
- PractiseLock it in on paper
- ReviewCome back and keep it sharp
- MasterTake on a harder challenge
- AchieveEarn a certificate
About Decimal Column Add Lab
Decimal Column Add Lab is about one habit and one error. The habit is writing both numbers with the same number of decimal places so that tenths sit under tenths and hundredths under hundredths — 12.4 becomes 12.40, and everything after that is ordinary column arithmetic. The error is what happens without it. Children have spent years lining numbers up by their last digit, because for whole numbers that is exactly right, and the habit carries straight into decimals where it is exactly wrong. Line 12.4 up against 3.75 by their final digits and you get an answer somewhere around 49.9 rather than 16.15 — not a small slip but a completely different number, produced by applying a well-learned rule in a place it does not belong. That misaligned result is offered as an answer option in every round of this game, deliberately. It is not a random wrong number, it is the specific answer a child gets by doing the wrong thing correctly, and offering it turns an invisible misconception into something a parent or teacher can actually see. The two numbers in each round always have different numbers of decimal places, because equal ones would let the whole lesson be skipped: line them up any way you like and the answer still comes out right. Both addition and subtraction appear from the third level. Free, no sign-up, no advertising to children.
Where to go next
Chosen by the skills this activity practises.
Next — more of the same skill
Printable worksheets for this skill
A hand for grown-ups
- Before you start
- Find a calm few minutes with no rush. Let your child know it is fine to find some of it tricky — that is what practice is for.
- While they work
- Sit nearby but let them lead. If they get stuck, ask "what could you try?" rather than giving the answer — the thinking is the point.
- Afterwards
- Ask them to show you one they found easy and one they found hard. Praise the effort on the hard one, not just the right answers.
- Watch out for
- Rushing. If answers come too fast and wrong, slow the pace down together rather than pushing for more.
- Away from the screen
- Look for the same maths in everyday life — counting stairs, sharing snacks, spotting shapes on a walk.
How to play
A question appears on screen
A maths question is shown in large text at the centre of the play area. A timer bar begins counting down from 120 seconds.
Choose the correct answer
Answer options are shown as large buttons. Tap or click the correct option. Any input method works — touch, mouse or keyboard.
Build your streak
Each consecutive correct answer increases your streak. A longer streak lights up the flame icon and adds a bonus multiplier to the XP you earn for the level.
Finish the level
Each level has 5 questions. Complete them to earn the full level reward (+10 XP, plus up to +10 XP for a perfect run). Progress is saved locally and shown on the Parent Dashboard.
Curriculum alignment
Mapped to national curriculum frameworks so teachers and parents can match practice to school standards.
- United StatesCommon Core State Standards for Mathematics · decimals, addition, subtractionAligned to decimals, addition, subtraction number and operations objectives.
- United KingdomNational Curriculum for England — Maths · decimals, addition, subtractionAligned to decimals, addition, subtraction number and operations objectives.
- AustraliaAustralian Curriculum v9.0 — Mathematics · decimals, addition, subtractionAligned to decimals, addition, subtraction number and operations objectives.
- CanadaPan-Canadian Provincial Standards · decimals, addition, subtractionAligned to decimals, addition, subtraction number and operations objectives.
Common questions from parents & teachers
Everything you need to know before your child starts playing.
- So the place values line up — tenths under tenths, hundredths under hundredths. After that it is ordinary column arithmetic.
- Children line the numbers up by their last digit, which is right for whole numbers and wrong here. 12.4 plus 3.75 comes out around 49.9 instead of 16.15.
- Because it is the exact answer a child gets by applying the wrong rule correctly. Offering it makes an invisible misconception visible.
- Yes, deliberately. If both had the same, any alignment would work and the lesson could be skipped.
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