I was trying to lay off Subtraction within 100 (involving borrowing over from the tens to ones) because i found it a tad too tough for my yet-to-be 5 year old to understand.
But he recently is into doing Word problems frenzy and we inevitably reached to subtracting within 100. That is when i reluctantly decided it was time to teach my little fellow.
I first taught him the Singaporean way, or rather the way i was taught. But i think i shouldn't have done that although he showed that he could do it. Still, i had him work on the Montessori Stamp game (which i personally think is THE BEST way to illustrate this topic) because i wanted him to be very clear about what it meant to 'borrow' from the tens to the ones.
So now, the sonny can subtract within 100. I dare not ask him to do it mentally although i vaguely remember he did it before. But i'm not going there, don't want him to be confused.
Very proud of you sonny, well done!