OP here,

yeah I thought not asking until I'm finished with this school too (since it ends in may already).

If it was some fellow student I would just have walked up to him or found some other tactics to make my move, but I find it so difficult to just randomly talk to that teacher after some months when I finished school and say:"...uh.. so I didn't have you in any subject but I saw you on the school grounds (maybe you've noticed me too?), care to go out with me?"

adives? ideas?

I seriously feel unsure about this although I'd really want to get to know him.