Hi Jamie,
I would consider you look at that book, but also that you get an evaluation done just for more information. A few things that you said make me think this. 1. You mentioned he has difficulty focusing but other times he can focus really well on things. That can be because of his interest level or that could also be a symptom of a child with ADHD because they don't just not focus, they tend to hyperfocus and focus very well on certain activities. 2. The difficulty getting sentences out. That is most likely because he has so much going on in his head he is having trouble organizing it all. Things move so quickly in there and there are so many thoughts his mouth can't even keep up and he can't put it into words. So...while this could be him being gifted, again it can be a symptom of a child with ADHD. Children with ADHD often have a hard time with organizational skills, have a lot of thoughts going on as well. I am not saying he has or doesn't have it obviously, but those two things you mentioned as well as the school concerns makes me think that it can't hurt to get an evaluation done. It will help you out either way. If he has it, they can give you suggestions and treatment. If he doesn't, then you will have information for the schools if and when the topic comes up. Win, win. Good luck!