Education Law Questions? Ask an Education Lawyer
What you describe is "false imprisonment".
I would recommend contacting a local civil litigation attorney to discuss your child's case and potential lawsuit.
Fortunately the majority of these attorneys will provide you with a free consultation, and many will represent you on a contingency basis (they will advance the costs of litigation and legal services in exchange for a portion of your successful settlement or judgment).
You can find local attorneys using the State and Local Bar Association directories, or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).