What can i do my child was molested at school and the principal and teacher doesnt take me seriously?

my child started preschool in august he comes home often with injuries like a busted temple a busted elbow a cut leg one day he came home with blood on the front of his pants i didnt think much of it cause ui figuredhe got into a scuffle with another child four days later my son tells me some one hurt his wee wee at school and made it bleed i then called the police they responded and went to the school where they were told there was no possible way for this to happen as my son has a monitor with him at all times i then pressured my child for more details and jhe told me it was another child i had a meeting with the school and discussed home schooling my child because of this matter i was then threatened by the principal saying she'd report him as missing if i didnt place him back in school i dont want to do this til i fing out who and why my son was molested and why nuthing is being done