I just commented on a similar post - but what I did before I went back to work was to pump a couple hours after I put my son to bed for the night. Or if I happened to get up in the night (to pee, or sleeplessness) I would pump a bottle or two out.
Also, if I fed him, and he was finished, about an 30minutes to 1 hour later I would pump the remainder out of my breasts.
Sometimes that only filled 1/2 a container, but I'd save it until the evening (in the fridge) to store up anymore I pumped, and at the end of the day I froze it. I believe you can contain milk for 24 hours in the fridge before freezing. But don't re-freeze after defrosting once.
At work I pump once a day (but that's the only missed feeding I do)... it's more difficult for you as a teacher, but at least try to do it when you can. As long as you breastfeed exclusively on the weekends, and when you're home with him at night, you should probably retain your milk! Good luck!