How the hell do you take care of tadpoles?

One of my students brought me a bunch of tadpoles, which irritated me at first but darn it, the little squirmers are just so cute! I bought a great terrarium for them and everything, made sure to have the student bring in pond water so they lived in their natural environment and changed it regularly. I even bought them special tadpole food (I'm such a softie). Unfortunately, they'd grow their back legs, then their front legs, then they go belly-up in their artificial pond. The last of them died today, having ignored all the tadpole food I gave them. Any ideas what I did wrong?