-snip-
That kind of shit normally happens to me...
So I've made it a habit of going to the teacher and letting him/her know that I'll be doing my job, but I won't play babysitter to anyone else.
I've also done this when I work.
I'll do what I was told, like get an area cleaned up/organized, and if nobody came back to do their bit...
I've gone to the boss and asked them what's next, because I've finished my part in the project.
Don't get me wrong, I let my team/coworkers know I'll do this if they don't pull their weight and I'll warn them before I go 'snitch'.
But there's no way in hell I'm risking my grade or my job because some people are stupid, lazy, 'tards.