I've never heard grind in that sense before either, that I recall. I might have guessed it meant a really hard assignment or course, a thing as opposed to a person; and now I'm not sure, maybe it can.
Surely there are quite a few threads in the archive on Streber, not just that one. flob21, did you try the forum search (Suche in allen Foren, at top left)? It no longer works with my browser (IE8), but if you can get it to work, you should find several past discussions.
An eager beaver isn't quite the same thing; it's not particularly for school and it's a little dated-sounding now. I think of it more as someone who's too quick to volunteer, panting to do something and be noticed, like a puppy.
A nerd has many of the same characteristics as a Streber, but the emphasis is more on enjoying hard subjects and finding schoolwork easy, and not being attractive or popular, but not really on just working hard.