I haven't gotten my DD tested and sometimes I doubt that I am right about her being gifted. She attends a public school and we do not have any gifted funding in our state so there is no advanced or acceleration. She gets 100 on all of her tests, her NWEA scores are 98/99 at every testing, she shows no growth because she is learning things she already knows somehow (I haven't been teaching her, she just knows a lot of stuff). Last night I asked her if she was excited about moving up to 4th grade and she said she was nervous about being bored all year long, which is the first time she has ever expressed this to me, although her 1st/2nd grade teacher (same teacher both years) told me she would finish her work quickly and distract others by talking, so she made her an enrichment packet to work on and keep her busy. Her 3rd grade teacher told me she would not do that. I told her I will talk to her 4th grade teacher and advocate for her to have the extra enrichment packet and that made her feel better. Yet I still find myself worrying that I am pushing giftedness onto her (probably because I receive so litte ... NONE... support from school that I start to question my own judgement because surely if a child were gifted they would acknowledge that.. but in truth, they won't).
Regarding your own son, even though he is in a Title 1 school I assume the curriculum has to be up to speed, so if he is completing that work with no problem or working a grade ahead with no problem, I am sure he is probably accelerated. If he is not struggling in 5th grade math this year, I would definitely let him go do the 6th grade math and at least give it a try. Better he tries and has to move backwards then never having the opportunity and being completely bored and under challenged.