Learning is one thing, but do not underestimate the effect of practice. I made an addition pyramids game for my seven and nine year old girls (Android) and prom

Learning is one thing, but do not underestimate the effect of practice. I made an addition pyramids game for my seven and nine year old girls (Android) and promised them a reward when they completed it (200+ levels, some 20 hours in total, progressively harder). After this my girls are able to do three digit additions in their heads without any major problems. Which means their "addition practice" homework from school has become useless. Which is a good thing I guess.