I experience block in the front of others

I experience block in the front of others i am 17 years old, i dont know how i cure my stammering, i start stammering when i was 6 years old than i make some success in curing of stammering, i got a lot of confidence, When I turned 14, than i start stammering again, i am facing block when i talk front of others mostly in class room, anyone can give advice how can i cure my stammering