I am assuming that the school didn't (and shouldn't) just relied on his DYS status for the acceleration. They must have provided to him some end-of-year testing where he demonstrated sufficient mastery as well. While I do not have experience with a double grade skip, DS did a double acceleration in 2nd grade from 2nd grade math to 4th grade math. Then in 4th grade, he skipped 6th grade math and studied Pre-Algebra instead. At the time of the initial double-skip, there were some issues with vocabulary and writing and the evaulator from the district office noted that he had his own unique way of solving problems probably because he was not taught the math that he would be skipping. In hindsight, these issues were minor so I wouldn't worry too much and just let him pick up what he needs naturally.
