The Duty to Report Possible Child Abuse
Every state in the United States currently has laws mandating teachers must formally report cases of possible or confirmed child abuse. Generally, the process begins with the teacher having a discussion with the school nurse or the principal about a possible case of child abuse. The next step involves filing a formal written report with the nurse or principal.
The nurse, principal, or other designee is then generally responsible for forwarding the report to the state's child-protective agency. Most of this procedural information will probably have been given to you beforehand, pursuant to your district's duty under state law to inform you of your responsibility to report child abuse.
Generally, state laws give you immunity from any criminal prosecution or any civil liability for reports that you make in good faith, which means reports based on a reasonable belief in the truthfulness of what you're saying. (Many states give immunity even in cases where you deliberately proffer a misleading or phony report.) The good-faith immunity you receive in all fifty states is sufficient to protect you from prosecutions or lawsuits.
As a matter of fact, if you do suspect child abuse yet say nothing, at that point you may well be subject to criminal prosecution under state reporting laws. Also at that point, civil lawsuits may become a real possibility if a child is subsequently injured — or worse — and it's learned that you could've filed a report and possibly prevented the tragedy.
The impetus for your filing a child-abuse report might be that you have personally noticed cuts, welts, marks, etc., on a child that reasonably lead you to believe that child might be suffering physical abuse. Written or oral evidence of abuse, given to you by a child, may also spur you to file a child-abuse report.
If you do begin the process of filing such a report, remember two things: First, do your best to record statements and observations carefully. Second, try not to be tortured by moral qualms about what you're doing. If a child truly is being harmed, then it's not merely your legal duty, but your sacred responsibility as a teacher to put an end to such an outrage. Trust in the law, and protect your kids.