Let me be blunt, if you are asserting that you had a past sexual relationship with a teacher who still working with children and you are aware of similar relationships with other youth, then you should be filing a complaint with local law enforcement authorities. You may want to discuss your concerns with a victims' rights advocate but the conduct you are describing is criminal in nature and should be reported to the appropriate authorities as soon as possible.
This advice is not a substitute for a thorough evaluation of all of the facts of your situation by an attorney in your community with a background in criminal law and child abuse matters.
Practically speaking, you cannot be assured of anonymity in this circumstance. Here is why:
If your report does not raise clear issues of improper conduct, then the school has no need or right to investigate or take any action. If that is the likely outcome, then there is little point to any report by you.
But, if your report raises issues of potentially improper conduct, then the school must investigate. The nature of the investigation will inevitably either reveal your statement and your identity or cause your identity to be discernible from the information revealed to the teacher by the investigation. In the event that the teacher were to be fired or disciplined by the State licensing authority, you would potentially be a witness, and in all events the teacher has rights to full disclosure of all evidence gathered in the course of the investigation on which the discipline is based. So, as a practical matter, either there is nothing to report or there is and your identity will be revealed. Please do not take that deduction as advice against making an appropriate report. It is not.
My responses to questions on Avvo are never intended as legal advice and must not be relied upon as legal advice. I give legal advice only in the course of an attorney-client relationship. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. That relationship is established only by individual consultation and execution of a written agreement for legal services.