If you homeschool you can probably do whatever you like - even if your children had to do standardised testing I'd be astonished if it cared what method they used. Fwiw noone (but me?) ever taught DS subtraction and I'm not sure what you'd call what he does! I do remember him saying with delight "we unwrap this bag of ten, and inside we fiiiiinnndddd...... Ten units!" at a certain stage!

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