The school may be able to help, but also document, document, document. And keep talking until you get the help you need. Take photos and start keeping it all in a journal or notebook. The more the evidence builds up, the harder it will be for them to ignore you.
It is how many parents change custody (including us) for any child.

Petition for sole custody. if his dad is abusing him, maybe he doesn't want to deal with him anymore.

Sweetie get an attorney and take him to court... document everything on a calender or journal plus the reports you have filed. I successful had my abusive ex-husbands parental right taken away. First they gave him supervised visitation that he had to pay for and he slacked of on making those visits and after a year then terminated his rights due to abandonment and say that he had made only minor token efforts to have any relationship with them. Also are there any police reports from his abuse of you and your older son.. if so use all of that in court. If your older son can and will have him testify. It will be a long road but worth it and most likely until they arrange supervised visits or other decision your son won't have to see him at all. It is well worth it in the end... Good luck

Hi I would take pictures before he leaves your house with a camrea with a date time stamp and when he comes home from dads document everything your son says how he is acting before and after his visits with dad but try not to use any leading questions and if posible have a witness to his behavior before and after not only to cover your self from aligations of abuse but to help the Child pretective services because this is what they are going to anyways details videos picture audio recordings send your son with a spy cam to dads or a voice activated recorder I hope this help god bless

I agreee with Maureen, document EVERYTHING! Take pictures with a date stamp, write everything down, and report every injury to the authorities. You can also hire an attorney and file a petition for sole custody of your son. Even if abuse hasn't been proven, all of the pictures and documentation of abuse will help alot in court. I'm not saying that he shouldn't see his dad, but make sure it is in a safe environment and supervised. Hang in there, and don't back down. You know what is best for your son!