LJ brain trust question

Several students at a yoga studio feel they have been touched inappropriately by the instructor. However, there is enough ambiguity for the instructor to have plausible deniability - that he was simply correcting their poses, as is part of his job as teacher.

What is the best course of action for these students to take to prevent other students from being harmed? Is there any legal recourse? Bonus points if you happen to know anything specific to California.

(No, I'm not one of the students involved in this.)