Do his interests interfere with his conversations with friends in that he only wants to talk about geography and lighthouses? Is he willing to talk with others about their interests or does he always try to bring the topic back to his interests? If so then I would work with him on this social skill IMHO.
I would also try to cultivate other interests for him as well by reading other topics to him and watching other shows on other topics.
My ds wants to talk about many things that kids his age are not interested in such as astrononmy, sub-atomic particles, evolution, etc.
I have to give him concrete examples of conversation topics for kids his age (8 years) on a regular basis such as Star Wars, Pokemon, Legos, Avatar, etc. which also interest my ds. I also have found social skills videos useful for him since he is a nerdy genius
