Considering the amount of nonsense I got up to in 11th grade chemistry lab including but not limited to lighting various metals on fire to see what colour they burned and handling hydrochloric acid, a little aluminum foil and toilet bowl cleaner should have been met with a slap on the wrist and possibly a talk from someone in the science department about what mixing chemicals you're not familiar with can do.

It was definitely not a smart choice to do it at school, and she was definitely aware of the fact that what she was going to do was going to go bang. Allowing for that, though - kids are curious, and with the advent of the Internet, if a kid's curiosity is piqued enough by something they saw on YouTube, I expect they're gonna try it, whether it's a Drano bomb or Mentos in Diet Coke.

Were I the teacher I'd have provided a controlled demonstration of why not to do things and some resources for experimenting safely. Expelling the poor girl just discourages her from experimenting with anything ever again.