I guess I had minor achievements in school, I never was top of the class or found anything easy. However, I do suffer from severe lack of confidence to the point where I won't even bother trying things because I assume I can't do them
For one, I think it's hard for us not to see ourselves in our kids... but if your ds has confidence issues, I think this is going to be your challenge... Don't equate intelligence with achievement, and encourage ways to be less failure averse.
Since a lot of kids have asynchronous development, where they are outrageously advanced in one area, they may be equally behind in another. It is my personal belief that a strong component in building confidence is building courage... the ability to look at failure as a learning experience, and to keep going.
When your ds fails at something, how do you approach it? Have you exposed him to some great minds that talk about failure? Edison, perhaps? What about going through some scientific studies and showing him the amount of wrong turns and well formed hypotheses are wrong through experimentation?
