Well, I can tell you our experience so far. DS is in 2nd grade.
There seemed to be no differentiation in first grade. DS really wanted to learn more math and mid-year said he hated math class because he was so bored. DS tried to work ahead in math to alleviate boredom and would get in trouble. At one point, he was being made to re-write his reversed letters when he got finished early in math (he's dysgraphic and has EDS which writing hurts his hands and fingers), which was really bad b/c he felt punished for mastering the concept quickly. He started feigning sickness to get of school and particularly math class. When I repeatedly approached the teacher about this and eventually the iep team, I was told they do "differentiate" but teacher kept finding reasons that DS didn't really need differentiation, that he really wasn't advanced, etc. Her main point during an iep meeting was that DS is competent in math and his 100% on tests proved she was teaching him not that he was ready for more difficult work. Her main theory was that DS "needs/wants to feel special" and "feel advanced" and if we just give the same on-level work and tell him it's more advanced that makes him happy (despite her thinking this was the case she was not actually fooling DS at all, he was on to her completely but didn't want to hurt or feelings or be disrespectful). She said he was bored because he has ADHD not b/c he truly bored with the math material. Worse - the principal piped up that they had a 1st grade child once who could trigonometry (or something like that) and that *that* was advanced - and *that* not my child (he said they did differentiate for that child). He said otherwise they do not group ability in math until third grade. I realized that the "poof is in the pudding" approach would get us nowhere and meanwhile my kid's achievement was staying solidly average, he was bored and depressed and was conflicted in that he felt capable of more and teachers kept telling him he wasn't. Not sure how much of a school mindset it is/was, if there really is intent to keep kids the same or if teacher really believed that DS didn't need more but I made enough of a fuss that she did set up a "math center" allowed DS and others to participate in that when they finished early in math (which was like all of the time). DS loved it - he and some other boys who were really interested in math would get together and pick a topic to work on (multiplication, division, square roots, etc). DS learned a lot believe it or not and started teaching himself stuff at home on the computer as well. I also started him on mathnasium because I walked away from that iep realizing that school and teacher were adamant about creating a ceiling for DS and keeping him at all costs at a certain level. He really wanted to learn more and I couldn't help him. He lOVES mathnasium.
Within a matter of a few months DS went from 60% in math on WJ-III to 95%.
Now in second grade things are looking up. DS took a pre-test and qualified for a math differentiation group that pulls kids out twice a week for special differentiated math instruction. It only just started (one meeting) but DS is optimistic and likes it. His WISC-IV score quailified for ATP but he only starts on Wednesday so we do not know how it is yet.
Pull-outs for differentiation and even remediation JUST started at our school. How "good" the differentiation will be - I do not know yet.
