I agree with MyZet. My son was exactly the same. Speech therapy, OT and always teach in small bits. Example.... my son never learned hus colours until he was 5. Turned out that he could tell the colours if u showed him only three at a time. If u showed him any more than that, he was overwhelmed and couldn't do it.

DD's diagnosis is high-functioning autism rather than PDD, but I highly recommend reading "The Autism Book" by Dr. Bob Sears and "Healing the New Childhood Epidemics" by Dr. Kenneth Bock. Traditional therapies like speech, OT, PT, behavior therapy, social skills training, etc. are certainly important but the gains we've seen from them have been of the "slow and steady" kind. Whereas we've seen dramatic jumps in functioning literally within days of adding certain biomed treatments.