For an in-class situation one I recall reading about. Physics problem, it gave the details of the stadium and how the ball was hit and asked if it was a home run. Foreign student was stumped, asked the teacher about it. The teacher was working through the problem with him, he understood everything--so what's the problem? "What's a home run?" Had that been a test rather than homework he would have had a 50% chance of getting it wrong due to a lack of sports knowledge rather than a lack of physics knowledge.