help with our new son

We recently adopted two children from Ukraine (and already had a third at home), our son is 6 and his sister will be 2 in June. Our son is extremely active and is into everything. He was labeled as hyperactive in Ukraine, but did not have any other behavioural/neurological problems listed. He is very disruptive at home, he will not listen when you ask him to stop doing something, we have found him out in the street a couple of times and he's very aggressive with other children and dogs. He seems to like school, but does not like being told what to do by the teacher and she has caught him cutting his hair twice already.He has been in school for about a week and the ESL facilitator and her son (who is fluent in Russian) came to the school yesterday to do an assessment of how much he knows. It turns out that he seems to have a lot of problems. He cannot count, does not recognize any letters, shapes or colours. He said he does not have a brother or a sister and he says his mother is Mrs Deer (his teacher). The only person he can identify is his Dad. They asked him if he likes to look out of the window and he said he didn't know what a window was. He says they had no windows in the orphanage and that he has been to school before, but can't say anything about it. He also said he did not know where he was, it wasn't school but that he liked it. He also has an extremely limited vocabulary and in addition to his speech impediment, he essentially just babbles. I know that children in Ukraine do not go to school until they are 7, but I would have thought he would have had more of a grasp of basic concepts than he does. We are going to take him to get an evaulation done at a behavioural clinic that specializes in IA children and we have our first pediatrician visit next week with a doctor that only sees IA children, hopefully we can get more of an idea of what is going on then. I am wondering if he really is severely delayed or whether he is just getting used to a new life. He does not seem that bad with respect to understanding, he's already picking up a few English words and is beginning to write his name, which I thought was pretty good after only a week.