I am unable to give you page numbers because I don't know what edition of the story you are using.  However, I will begin the quotes starting at the paragraph that begins "his schoolhouse" (paragraph 9). 

"He administered justice with discrimination rather than severity, taking the burthen off the backs of the weak, and laying it on those of the strong."

This quote means that Ichabod was biased in how he dealt out discipline.  If a child was weak and cried, he would avoid striking that child (the common discipline in those days) and would give the whacks to an older, stronger child. 

"He was even the companion and playmate of the larger boys; and on holiday afternoons would convoy some of the smaller ones home, who happened to have pretty sisters, or good housewives for mothers, noted for the comforts of the cupboard."

So he used to free time to "play" with his students, as if a friend.  He also walked home the smaller children, but only if they had pretty sisters or their mothers made good food.

From these two quotes, there is some suggestion that Ichabod was an unfair and devious teacher, and not very competent.

Ichabod's disappearance was likely flight.  He had been disappointed in his hopes for Katrina, and now his imagination has led him to believe in the spirit of the demon horsemen.  Not a very strong man, it is easy to assume he left town in embarrassment and fear.