You need to take immediate action on this matter!
First, Print off this thread and show it to her!
If she does not care to read it, read it to her!
After reading this thread, and she still does not want to take your advice or generosity in buying her a new tank, then I would threaten her that you are going to report this to higher authorities!
I mean, come on, if there was like a pet hamster, cat or dog in the class room (just as an example), and those animals where being kept in a small cage all day with poor living requirements, (lack of space = lack of water for fish), (having the animal live in their own waste = uncycled tank), I think there would be some major issues on hand!
The thing is, goldfish, or any other fish for that matter, are seen to people like you teacher as a "come-and-go spur-of-the-moment thing."
She probably thinks that since these fish look okay, based on her knowledge of fish care, then they probably are okay. And if they do die, "who cares, they are cheap and I can some new ones for a couple dollars."
Inchyally, you need to take action at the next possible moment, or I will personlly talk to your teacher face-to-face and tell her whats up! lol
This just seriously ticks me off! You read about it and watch videos of it on youtube, but if you actually are witnessing it and can do something about it, then by all means do something about it!
-FHM