UKEdMag: Calculation Races by @ThisIsLiamM

Mental versus written multiplication

Earlier this week, my class and I were undertaking a Number Talk. The question we were using was ’19 X 24′. I hoped many children (mixed ability Year Five) would use a mental method or jottings (partitioning, rounding & adjusting and so on).

However, over 90% of the class used a grid method or expanded column multiplication. Nothing wrong with that, except the focus we’d been having on mental methods and not always defaulting to a written method. We listened to how children had arrived at their answers and then discussed which were the most efficient. As a class, we then solved both 19 X 28 and 19 X 35 using rounding (20 X 28) and partitioning (10 X 35 added to 9 X 35) to remind them of the available less formal / mental / jotting methods available to them.

In order to win over the remaining doubters I still had in the class, I set the children a challenge. They’d solve a question using only mental methods, while I tired to answer it as a written method on the classroom whiteboard. Although I wanted to prove the mental method was quickest, I still tried really (really, really) hard to do my method quicker than the class. However, I ‘lost’ all three times (19 X 56, 19 X 45 & 29 X 34). I’d only got beyond setting up the method and doing the first part of the calculation.

Class won over!

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