the act of teaching at school
"The teacher spent the afternoon helping students catch up on their schooling after they missed several weeks due to illness."
the training of an animal (especially the training of a horse for dressage)
"The young horse required several months of schooling before it could successfully perform complex dressage movements."
Training or instruction.
"The new pilot received extensive schooling before being cleared to fly solo missions."
present participle of school
"The fish swim together in their daily schooling patterns across the open ocean."
In plain English: To school something means to train it by teaching and guiding its behavior over time.
"The parents are currently schooling their children at home instead of sending them to public classes."