Fat-Tails I've found are a very hardy gecko. Being your getting an established adult, you shouldn't have any problems with him/her.
My adult Fatties usually only get fed twice a week. Sometimes three or even sometimes once per week. Each feeding consist of about 6 to 10 larger crickets. They all keep on good weight with this routine. You can even do less crckets per feeding with more frequent feedings if you prefer.
Being both my parents are teachers, I somewhat understand what a teachers schedule is like. He/She will be just fine over the weekends & even over any breaks that are a week long. Any of the breaks that go over two weeks, I would concider taking the gecko home with you.
Good luck & enjoy the new edition to your classroom.