Then let the children feel that learning itself is a happy thing. If they eat well, sleep well and have a good rest, they are in good health and mental state. They only need a little guidance, and naturally they can concentrate on their studies and enjoy them. The same is true of mathematics. They can prepare a wrong problem book, extract the problems they don't know or do wrong, and take out the problems in the wrong problem book for him to do every once in a while. They won't pick them out again, but they will do it after a long time.