I'm a teacher, and I can be pretty brutally frank with children when they need it. Explaining to somebody that they are going to lose points in a test because they mucked around, and that it must not happen again or the test will not be corrected, is not a situation that calls for a "there, there, it'll all be alright, luv." On the other hand, trying to get a 16 y.o. to understand that English is arguably the one subject that he will really need (I teach in France) when he finishes his education and is looking for a job, requires a lot more tact.