I skipped a whole grade (7th) when I entered a GT school with an accelerated curriculum. When I returned to public school in 11th grade, I was placed in some senior courses like Calculus and 4th yr German. I then "ran out" of math and German so I ended up taking a bunch of electives to fill my schedule the next year.

DS skipped to 1st from K in the spring last year. He is now in 2nd and doing well. We are considering subject acceleration in math to 3rd.