Grabbing someone by their shirt? Is that considered assult?

An assualt is basically putting the victim in fear of an offensive imminent attack or contact. Battery is the actual offensive physical contact. Grabbing a shirt is really a battery, but most police would refer to it as an "assault." Bottom line is that unless it was self defense the boy doing the grabbing has likely committed a criminal act. Yet these things happen often in schools and do not always rise to the level of an arrest. Your question "can charges be filed?" Likely, yes.