I have two boys who had autism spectrum disorders, but don't, anymore. That's not because they were misdiagnosed, and I do not believe it was because they were "cured" of PDD-NOS. I believe that it is very, very hard to diagnose children. I think that ADHD and bipolar disorder are the diagnoses du jour. That does't mean that the symptoms aren't real, it means that they should be diagnosing and treating the family as a whole, not just one child.
That being said, that doesn't mean that your child doesn't need medication. But if a child is having difficulty to the extent that medication is a viable alternative, the whole family should also go into counseling. In fact, if you were taking care of a parent with Alzheimer's disease, the whole family should go into counseling. There are issues that crop up whenever a beloved family member is suffering, if nothing else.
My three-year-old was engaging in life-threatening behaviors, and I had him on three psychoactive medications at once. His quality of life skyrocketed. He made astonishing improvements. He's now five years old and he's been off meds for a year. But we've decided to put my older child back on meds because his psychologist says that he would benefit from medication that assists with concentration and focus.
When medication helps, it really, really helps. You may need to try more than one medication. But that is not the end of the inquiry. The whole family should work together on behavioral issues, and on maintaining balance, and to help him.
Make sure that, if he is getting medication, he is also getting psychotherapy. Make sure also that you apprise the school of what he is taking. They can tell you how he's doing during the day, and also if he breaks his ankle in gym class and needs medical attention, the school should be able to tell the paramedics what he's taking.
Good luck!