Child derailing my son's classroom

There's a kid in my son's classroom that is so far behind developmentally/emotionally it's shocking.I don't really know if it's even diagnosable, but it is very odd. Just by looking at his face, his height, his hands, his voice and behavior, I would say he looks and acts like he is 3 if I didn't know any better. He is actually 6.I am the class mom and I help read with the kids, and I'm also a member of the parents' group that runs events and volunteers around the school so I am at the school every day and in the classroom quite a bit.I have ADHD and so does my son, but when I say this kid is off the rails I don't mean that he is hyperactive. He just is not ready to be in school. He wanders around, doesn't follow directions, makes silly voices and noises, is constantly launching himself into people and hugging them--literally this kid is so sweet but is on a whole other level. The other kids don't like him because the attention he gives them is SO INTENSE and no age-appropriate.The teacher is at her wit's end. He derails entire lessons sometimes. Thank god there's an assistant because I have no idea what this poor teacher would do without her.At least now the kid can get his backpack in his cubby, at the beginning of the year he'd come to school so excited, drop his shit on the floor, wander around, give hugs to half the class, talk to people, all the while oblivious to the assistant and teacher yelling his name to get his attention that his bag was in the hall. Then he wouldn't put it away because he didn't want to.I sometimes volunteer for lunch and recess duty and this kid is so sweet but something is clearly abnormal. He acts like a toddler. He even ran away and snuck into the preschool class.Is this normal? Can some kids be this behind developmentally? With potty training and language he seems to be reasonably on target...I guess....but his reading comprehension is about where my 4 year old preschooler's is. He can sometimes sit through part of a story and sometimes answer questions about what is happening, but he is far behind his peers. He acts and LOOKS--physically looks like a 3 year old.This is a private school with no psychologist or support services. I'm upset that the school has allowed him to stay because he is clearly not ready for school and not a good fit, and his behavior impacts the entire class.Is there something I am missing? Is this normal? Should I or can I go to admin about this? I feel bad because the kid is really so sweet but he's just...oh my god he's just a hot mess. He must be under so much stress in this environment. Is this like a diagnosable thing? via /r/Parenting http://ift.tt/2F8PyD8