When you first go to school it is all very new. You meet new people, grown ups and children, there is a discipline where you have to sit still and be quiet, not run about and talk all the time. Then you have to learn the alphabet and numbers. Girls in general get switched on straight away and quickly learn to do what is required. Throughout the rest of their school days they do the required work and fit in to the system.
Boys tend to take longer.
They like to play with their friends and form gangs. School is a place where they meet their friends and muck about. Work is a dirty word. The general tendency is to do the minimum work that you can get away with. Homework is done in a hurry in the minimum time and never checked.