DS in 2nd grade went to 5th grade for math, until the teacher said he didn't need to go anymore because he was done with it. He twiddled his thumbs the rest of that school year.
In 3rd grade, we tried ALEKS, starting him at the beginning (3rd grade level) to make sure he hadn't missed anything, and he did 3rd-4th-5th-6th and half of 7th before Christmas break. He burned out at that point and only finished another 25-30% of 7th grade in ALEKS that spring.
In 4th grade, he had his own private math tutor, a paraprofessional who took him out of class when they were having math, and he manipulated her and the high schoolers who came in periodically and ended up still not finishing 7th grade math that year. It was most disappointing.
This year, in 5th grade, he took 7th grade advanced math class at the Middle School, and will be moving into 8th advanced next year as a 7th grader (skipping 6th because he took most of it this year).
So we telescoped 3rd to 7th in one year, then spent two more years on 7th. I'm still not happy with where this has left him, because his teacher says he is bored with it all (wonder why?) and he really could be so much farther along if not for some missteps and his general lack of ambition. He doesn't feel motivated to work ahead anymore, like he did years ago, and that makes me sad.
I would recommend telescoping everything you can, while there is still interest, and maybe it will stay.
