My state won't let you do that, so I haven't thoroughly thought it through. If they would, I'd be completely in favor of it for my DD.
- You're compared against your agemates for talent search.
- You aren't precluded from doing camp that requires a certain match of grade and age
- You aren't fast-tracked out of high school, with your college choices limited either by age or ability to live independently far away, but can dual-enroll to get the higher level of challenge
- You can leave high school with a diploma based on high school level courses taken if that seems like a better idea
It takes some planning to get your NMSF eligibility right. (It works out funny when you leave high school at the wrong time, such that you might entirely miss out on National Merit scholarships available only to entering freshmen.)
Dual enrollment in my state requires you take at least 2 high school courses each term, and at some point, you may run out of courses worth the time.
It may be administratively difficult for the school, if Class X is limited to kids in Grade Y, or if the scheduling in general makes cross-grade enrollment difficult.
