Speaking at School

Hes 15, im sure he can plan what to say himself, the issue expressed is not in knowing what to say but in overcoming the inhibition. Id suggest you find the least difficult circumstance and have a go. If you still have difficulty, you could try the turn and talk technique by which you wait till you hear a comment that you would be comfortable discussing then turn to the person/group and make a response to what has been said. 

To be avoided however, is going around attempting to start conversations about your "special interests" as this is unlikely to prove as interesting to others as it does to yourself and can result in open mockery and deliberate exclusion.

Hes 15, im sure he can plan what to say himself, the issue expressed is not in knowing what to say but in overcoming the inhibition. Id suggest you find the least difficult circumstance and have a go. If you still have difficulty, you could try the turn and talk technique by which you wait till you hear a comment that you would be comfortable discussing then turn to the person/group and make a response to what has been said. 

To be avoided however, is going around attempting to start conversations about your "special interests" as this is unlikely to prove as interesting to others as it does to yourself and can result in open mockery and deliberate exclusion.