I was much like this as well during my time in high school and throughout much of middle school. In elementary school, most didn't care, but in the higher grades, when students became much more judgemental, it became a problem for me. Just like you, I was perceived as the intelligent student of the bunch, and I too was also worried about ruining such a reputation via my impediment. During the end of high school, I had gotten the hang of talking clearly and unimpeded, but only in short bursts, mostly because it was easier to talk more freely with friends or trusted individuals with whom I had no fear of embarrassing myself. To this day, I've never overcome my stutter entirely, but I found that the more I avoided social interaction, and the more I anticipated experiencing a speech block or the like, the more I ended up doing so when push came to shove and interactions were unavoidable. I can't claim to be an expert, but I think you should avoid anticipating embarrassment or incompetence, and begin believing that you can, in fact, speak with others in a manner befitting one of your own intelligence. People who share your intelligence will likely be able to see past your impediments for who you really are.