If I could give no stars, I would. The acting is mostly terrible except for Elizabeth Rohm. Notably terrible things: 1) the blond teacher is played as a ditz and the one black male actor is the bad guy -- which just reinforces negative stereotypes. 2) the 12 year old girl first becomes a mermaid and then becomes a murderer -- and no one seems to care when she kills the lone black actor and then calmly steps over his clothes with a smile! In fact, all the actors in that scene let the girl kill this man and then they all walk away. There's also the weirdness of her saying humans are 65% water, and then when the bad guy "melts," nothing is left besides his clothes. Did the writers not know how to do their math? Surely there is another 35% to account for!
This is a terrible movie for young girls to watch.