Looks like I sway against the hives opinion on this one but I'd say it depends on your relationship with the boss. I think they would appreciate the forwardness of honesty and the savings on your recurrent training.
A coworker was talking behind the bosses back about his near departure. Once he found out the person was let go on the spot. On the other hand I gave him plenty of notice that I wouldn't be going back to school and it didn't hurt the last 6mo here. I've even been offered contract work in the future.