Ask any primary school child what their least favourite part of maths is and the answer is almost always the same: “doing it in my head.”
Mental maths is one of the most tested skills in KS2 SATs and the Eleven Plus — yet it’s also one of the most overlooked areas of preparation. Children spend hours on worksheets and past papers but rarely practise the kind of quick, confident mental calculation that actually saves precious minutes in an exam.
At Spot On Learning in Feltham, we teach these tricks to every KS2 student we work with. Ten minutes of daily practice is all it takes — and the results speak for themselves.
Here are the 10 mental maths tricks that consistently make the biggest difference.
- The “Rounding and Adjusting” Trick for Addition
Instead of adding two numbers directly, round one of them to the nearest 10, add it, then adjust.
Example: 47 + 38
Round 38 up to 40 → 47 + 40 = 87 → subtract the 2 you added → 85
This works brilliantly for any addition where one number is close to a multiple of 10. Once children get comfortable with it, they can apply it almost instantly.
Practise it: Give your child five addition questions at bedtime. No pencil, no paper — just thinking aloud.
- Doubling and Halving for Multiplication
When multiplying two numbers, if one is even, halve it and double the other. The answer stays the same.
Example: 16 × 15
Halve 16 → 8. Double 15 → 30. So 8 × 30 = 240
This turns a tricky multiplication into a much simpler one. It’s especially useful in SATs papers where mental calculation speed is key.
- Multiplying by 9 Using Your Fingers
This one is a favourite with younger KS2 students — and it genuinely works.
Hold up all ten fingers. To multiply any number (1–10) by 9, fold down that finger. The fingers to the left give the tens digit; the fingers to the right give the units digit.
Example: 9 × 7 → fold down finger 7 → 6 fingers left, 3 fingers right → 63
It sounds too simple but it sticks in children’s memories far better than rote recitation.
- The “Multiply by 4” Shortcut
Instead of multiplying by 4 directly, double the number twice.
Example: 23 × 4
23 × 2 = 46 → 46 × 2 = 92
This keeps numbers smaller at every stage, which reduces working memory load — exactly what you want in a timed exam.
- Subtracting by Counting Up
Many children find subtraction harder than addition because they try to “take away” in their heads. Flipping it to a counting-up problem is far easier.
Example: 83 − 47
Count up from 47 to 83: 47 → 50 (that’s 3) → 80 (that’s 30) → 83 (that’s 3) → 3 + 30 + 3 = 36
This method — sometimes called the “shopkeeper’s method” — is intuitive, fast and almost error-free once practised.
- Multiplying by 11 (the Fast Way)
For any two-digit number multiplied by 11, add the two digits together and place the result in the middle.
Example: 11 × 36
3 + 6 = 9 → place 9 between 3 and 6 → 396
If the two digits add up to more than 9, carry the 1 into the first digit.
Example: 11 × 78
7 + 8 = 15 → place 5 in the middle, carry 1 → 7 becomes 8 → 858
KS2 children absolutely love this trick — it feels like a magic trick rather than maths.
- Squaring Numbers Ending in 5
Any number ending in 5, when squared, always ends in 25. Multiply the first digit(s) by the next number up, then add 25.
Example: 35²
3 × 4 = 12 → add 25 → 1,225
Example: 75²
7 × 8 = 56 → add 25 → 5,625
This comes up more in 11+ maths papers than SATs, but it’s a fantastic trick that builds number confidence at any level.
- The “Percentage Swap” Trick
Finding 8% of 75 feels hard. But percentages work both ways — so swap them.
8% of 75 = 75% of 8 = 6
Finding 75% of 8 is much easier: 8 × 0.75 = 6, or simply half of 8 is 4, plus a quarter of 8 is 2, so 4 + 2 = 6.
This trick works for any percentage and is a genuine time-saver in KS2 SATs reasoning papers.
- Breaking Down Tricky Multiplications
When a multiplication looks too big to do mentally, break one number into parts.
Example: 14 × 13
Split 13 into 10 + 3
14 × 10 = 140
14 × 3 = 42
140 + 42 = 182
This is essentially the grid method done in your head — and once children are comfortable with it, they can tackle almost any two-digit multiplication without writing anything down.
- Estimating First, Then Calculating
This isn’t strictly a calculation trick — it’s an exam technique that saves children from costly errors.
Before working out any answer, quickly estimate what it should be. If the estimate and the calculated answer are far apart, something has gone wrong.
Example: 312 × 19
Estimate: 300 × 20 = 6,000. So the answer should be somewhere around 6,000. If your child writes down 592, they know immediately to recheck.
We teach every Spot On Learning student to estimate first. It takes two seconds and catches a surprising number of mistakes before they’re committed to the answer line.
How to Make These Tricks Stick
Learning the tricks is the easy part. Getting children to use them automatically under exam pressure is the real goal. Here’s how we recommend building the habit:
Daily 10-minute practice. Set a timer and give your child 10 quick mental maths questions every day. Vary the question type so all 10 tricks get covered over the course of a week.
Think aloud. Ask your child to explain their method as they answer. This builds metacognitive awareness — they start to choose the right trick for the right question automatically.
Make it a game. Apps like Prodigy, Times Tables Rock Stars and even simple card games build mental maths fluency in a way that feels nothing like revision.
Reward speed, not just accuracy. In KS2 SATs and the 11+, time management is everything. Celebrate when your child gets faster, not just when they get it right.
When Practice Isn’t Enough
Sometimes, despite consistent effort at home, a child’s maths confidence just isn’t growing. That’s usually a sign that there’s a specific gap in their foundational understanding — not laziness, not lack of effort, just a concept that was never fully locked in.
That’s exactly what our KS2 maths tutors at Spot On Learning are trained to find and fix. We assess every student individually, identify precisely where the gaps are, and build a personalised lesson plan around them.
Many of our KS2 students move up sets in school within a term of starting with us — and several parents have told us their child went from dreading maths to actually looking forward to it.
Frequently Asked Questions
At what age should children start practising mental maths?
From Year 2 (age 6–7) onwards, simple mental maths — adding single digits, counting in 2s, 5s and 10s — is appropriate. By Year 4, children should be working on all four operations mentally. By Year 5 and 6, all 10 tricks in this article are fair game.
Will these tricks help with the 11+ as well as SATs?
Absolutely. Both the SATs arithmetic paper and the 11+ maths paper reward fast, accurate mental calculation. These tricks are useful for both.
How long before my child sees an improvement?
With consistent daily practice, most children show measurable improvement in speed and accuracy within three to four weeks. Confidence tends to follow shortly after.
My child uses their fingers to count — is that a problem?
At KS1 level, no. By Year 4 and 5, it does slow things down significantly. The doubling, halving and rounding tricks in this article are specifically designed to replace finger-counting with faster mental strategies.
Final Thoughts
Mental maths isn’t a talent some children are born with — it’s a skill built through the right strategies and consistent practice. With these 10 tricks and ten minutes a day, your child can walk into their KS2 SATs or 11+ paper with genuine confidence.
If you’d like your child to benefit from personalised maths tutoring in Feltham, we’d love to help.
📍 Spot On Learning | 2 Sherringham Avenue, Feltham, TW13 7JT
📞 +44 7577 580634
✉️ info@spotonlearn.co.uk
🌐 www.spotonlearn.co.uk
Add comment