Do I have a case for educational malpractice or something else?

Hi. We have a 5yr old in preK. He's been at the same school for 3 years (he went to preschool there). This year he started having significant behavioral problems (aggressive hitting/biting, etc) The school said they did not think he needed a DOE evaluation, but we requested an evaluation anyway-- he has an IEP, with SEIT and OT services and play therapy. His behaviors continue to be a problem, and so he was recently kicked out of the school's after school program, and so my wife has had to cut her work hours. Surprisingly to us, the school is telling us now that he's had problems for years. We can't help but wonder why the school didn't let us know about any problems before this year, and if there were problems why they didn't recommended an evaluation. Perhaps we wouldn't be in the same situation we are in now if there was an early intervention. Is this educational malpractice?