That's probably true. There are probably some cases where that still happens, but the normal procedure is to do your endowment a few weeks before you leave on a mission.
There are a few rare exceptions where the kid is coming from a foreign country where there isn't any good access to a temple, and he was called to serve a mission in the states. Then they can decide to have him come to the MTC and just get his endowments at the Provo temple. It is very rare though.