present simple: Jerry doesn't "teach" maths at high school. Simply saying that that is not what Jerry does. It has no connection with the past or future. Maybe it is in response to someone suggesting that is what Jerry's job is, so you are giving them the correct information. Jerry hasn't taught math at high school. There is a connection with the past here. the statement is 'true until now'. So perhaps you are discussing whether Jerry is able to do this. The reason for the tense is that it tells us Jerry never did this before. Perhaps he only taught it at middle school, or maybe he lied about doing it :)