I just read through the 1st Commandment part of the Catechism and I would say that hypnotism is borderline with that. It does talk about magic and sorcery and all that in the Catechism, but not hypnotism explicitly. I suppose it could be another form of control where the hypnotist usurps God, but if the intention is lacking in taking the place of God then I do not think it is a violation of the 1st Commandment.
Regardless, attendance at a hypnotism assembly should not be required. I think there are better things that school should be doing with your tax dollars. You pay for them to get an education, not Las Vegas style entertainment.