For subtraction facts use my "add to subtract" method for teen numbers minus 9 through 5.
Here's an example 17-8. 17 is a 10 and a 7. I can't take 8 from 7, but I can take 8 from 10 (child probably knows 10-8=2). So when I do (10-8)+7 I get 2+7=9. Once they understand how this works show them the shortcut. Whenever I am subtracting 8 from a teen number I can just look at the ones digit of the teen number and add 2. So I see 17-8 and I think 7...8,9.
There's even a pattern of what you add to subtract.
To subtract 9, add 1
To subtract 8, add 2
To subtract 7, add 3
To subtract 6, add 4
To subtract 5, add 5
You add whatever goes with the number you're subtracting to make ten.
