meaning of OUT as in "ACTING OUT IN CLASS"
Solution 1:
In the US, at least --
"Act out", in this context, means to "act up" loudly/visibly. Ie, cause a disturbance. A very common term for describing classroom misbehavior.
It's an idiom, perhaps a blend of the two idioms "act up" and "shout out".
It's probably fruitless to attempt to apply a dictionary meaning to "out" in this case.