Maybe a little off-topic, but here is an interesting criticism of the newly-released DSM-5, including (about half-way through) a discussion of how for at least some disorders there appears to be significant chance of getting different diagnoses from different psych people:

http://online.wsj.com/article/SB10001424127887323716304578481222760113886.html

So I don't know what the answer is to which psych to believe, except the one that is best for your kid. But it does seem to be an area of great uncertainty, even among experts.