As we know, Holden was kicked out of schools several times. What do you think was the reason?

There are quite a few reasons why Holden might have been kicked out of the two schools that he attended before attending (and then leaving) Pencey Prep.  First, he may have suffered from the same bad grades that were about to get him kicked out of Pencey.  Holden tells the reader that he was failing four classes and was about to be kicked out but he decided to leave before that could happen.  This is one possibility.  A second possible reason that he was kicked out of those schools could have been his behavior.  Holden has difficulty getting along with many people and throughout the novel he makes many comments about getting into fights (even though he claims to be a pacifist).    This tendency to fight, argue, and simply not get along with others could have been the reason.  Finally, Holden is a perpetual liar.  It is also possible that his lying was to blame for him getting kicked out of school.