Where do i stand? What can i legally do?

Where do i stand? What do i do?
My 9 year old son has been struggling so much at school over the last year and a half.
He has a diagnosis of ADHD and ODD
My ex and i have shared care of our 2 children. Week on week off.
We have tried sports, counselling, play therapy because my ex is too stubborn and doesn't believe in medication for children.
My son struggles to make and keep good friendships at school. His school work is suffering majorly due to his inability to be able to concentrate and focus. He's constantly chatting and being disruptive and often leaves the class to cool down.
His self esteem is suffering because he thinks he's dumb. He has mentioned wanting to tie a rope around his neck.
My ex and i seperated 6 years ago due to me not enabling him to control me anymore, but i have always encouraged the kids to do week on week off with both of us as we are both their parents.
Had yet another school meeting today and they encourage the trial of medication as they really think it could help our boy.
Im all for this, my ex thinks he can dicipline the diagnoses out of our son and he wants our boy fulltime. Our children already complain that "Dad is always so angry all the time" I do not want our son living there scared full time.
Where do i go from here?
Family and children services?