Once in 5th or 6th grade we had a math homework of a few dozen problems multiplying 3 or 4 digit numbers together.

Totally tedious.

Instead of mindlessly doing it, I spent a few hours making a BASIC program that did the multiplication, but importantly showed all the intermediate steps that we were required to show (eg multiplying by 634 shows the multiplication by 4, 30, and 600 separately).

Writing that program took probably 3x as long, but I wound up learning 50x vs the rote multiplication we were assigned.