Prime Factor Decomposition

I have stopped using a Prime factor tree when teaching Prime Factor Decomposition and so should you!

Here's why:

1. Students mix up Frequency trees and Prime Factor trees.

2. Students don't always realise that the prime numbers are the 'building blocks' of the number and they just need to complete the tree to get the mark.

3. Incorrectly writing their final answer.

What I now do:

It still looks very similar but I have a big focus on rewriting the original number each time and using a line for each step of their workings.

For some students I have used little arrows to show which numbers need to be split further and underlined the prime numbers so they can more clearly identify what their next step is.

I explicitly teach about using the numbers to 'go backwards' and find other factors e.g. 3 x 2 x 2 = 12 which is a factor of 72.

I show students how no matter the starting point, we still end up with the same building blocks e.g. if we started with 2 x 36 we would still end up with the same answer.

I recently taught my Year 7 class this method and found a lot less of the 'classic' misconceptions coming up which gave us more time to explore the topic to much greater depth.

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Cameron Setter

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