Have you looked at camps for gifted kids usually held at universities? At that age my son attended a gifted camp held at a local university. He took a class in 'physics' and 'chemistry'. The classes were run by junior faculty and graduate students and labs were held in university labs. It was a good experience. I can PM the information about his camp if you want, although I don't seen the specific classes he took on offer this year.
It really depends on where you are located. Another place to check is a local science museum?
