What can i do to stop suspected retaliation after i voiced safety concerns?

I work at a public school.
Safety concerns were about lifting procedures for students (in our severe/profound ID classroom) and pattern of injuries inflicted on employees by students.
Retaliatory activities so far include but are not limited to the following: called into office several times for questionings and talkings-to, reprimanded for taking a walk during my break on school grounds, reprimanded for sitting in my car during my break (which had been done by several other employees who were not reprimanded), not given opportunity to assist in other rooms in spite of being the most qualified to do so (while those who did not complain and who give their time away had this opportunity). When I called attention to the last item, within a day or so I was called into the office and presented with a letter telling me I can't sit in my car during breaks and insisting I stay on the sidewalk if I walk outside. I have a picture of a pre-k class a few days later outdoors--they were not made to stay even close to the sidewalk. I fear they are trying to make it so that I don't want to work here (it's working) and won't be able to transfer or move up.