Subtraction

Subtraction has been a nightmare for my class this year.

We have used number lines in every possible way and concrete apparatus but nothing has really worked. Whenever I give them a problem or a calculation to solve involving subtraction,  most of them cannot arrive at the correct answer. If I go over a particular method before giving them the problems then it’s not too bad but it doesn’t stick. The errors aren’t uniform either. There doesn’t seem to be any pattern to the mistakes they make or reasons as to why they make them. The majority of the class just seem to be confused.

So in desperation I decided to show them how to do subtraction using decomposition. I did a couple of examples on the whiteboard and then got them to work some out in pairs using their mini boards. They were all interested and immediately got the connection with column addition which they are not bad at. There was a real feeling of excitement as they found they were arriving at the correct answers quickly.

I had one or two who still weren’t sure so the next day I did some more teaching, This time I used the idea of money and changing a 10p piece for 10 1p pieces and the actual amount of money staying the same. This visual image seemed to help them and they seemed much more confident. The rest of the class were all looking at subtraction problems and using the method confidently.

Today we did some further problems and every child got the correct answers!

I know that it is still fresh in their minds and that next week they may well forget and make the usual mistakes but I don’t care. They feel that they have cracked subtraction. They love using the new method and their confidence has soared.

Next week we will look at examples of when it is not a good method to use so they don’t get too carried away.

This is a real example of how useful an algorithm is if the children are ready for it. They really do seem to understand the process behind what they are doing and not making any of the typical mistakes that happen when children don’t truly understand. I almost wish that I had taught it earlier in the year but then the understanding may not have been there.

It was a lovely lesson to end the week on. I’m now ready for my weekend of maths on my MaST residential. The only real problem is having to get up at 6.45 on a Saturday morning!

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