When I was at school we were not allowed to speak French in class, even when it was to help immigrants who spoke no Hebrew. Jaffa Arabs speak Hebrew quite well enough not to need to speak Arabic in class, unless it is to disrupt lessons or make a point. Were it truly the matter of an occasional clarification, it would not have turned into a newsworthy item.
PM: We'll surround ourselves with fences in defense against the wild beasts around us (Haaretz)
from the article: Ban on Arabic in Jaffa classroom sparks protests