The answer likely depends on the school and the individual kid. Certainly, it is not “needed” to do double in science in 9th , and I agree for the vast majority of kids it is not ideal to start HS with that kind of intensity. However, one of mine did APStat(A+,5) in 9th (“doubled” in math), and doubled in science in 10th (Ap Chem and APPhys1). APs are not allowed in 9th–this was an exception initiated by the school due to being ahead, yet doubling science in 10th is not overly rare(4-6 kids every year). At the neighboring school, no “doubling” or APs happen before 11th and they seem to all do just fine. So…it just depends. Talk to your school but be careful not to get in over your head so early in HS.