My son (DS 10, 5th) was in private school from Kinder to 1st grade. He's been in a parent-participation K-8 public charter school since 2nd grade.
None of the schools that our son attended has GATE program, hence no gifted testing. We were also oblivious to the gifted issue and only last year were 'introduced' to this. Our son has since been tested and we've been advocating for him.
Although the school doesn't offer GATE program, they do differentiate through ability grouping. We have Math Mix-up in Kinder/1st grade, 2nd/3rd, and 4th/5th. However, since math is not done at the same time across grade level, there can be tricky scheduling issues when a child needs to move up above their combo class level. It becomes even trickier when elementary students need to move up to middle school math.
That being said, our son was pretty lucky since he got an excellent teacher in 2/3 grade (it's a combo class, and the kids stay with the same teacher for 2 yrs). He was able to do 3rd grade math in 2nd grade. When he couldn't go to 4th grade math because of scheduling issue, she continued to challenge him in her own classroom.
Our daughter's teacher (DD6 - not tested) is amazing, too. She grouped her students (K/1 combo class) based on their ability in reading, writing, and math. She has some of them working on 2nd grade reading and math. At the other end, she also has kids who are still learning their letters and numbers. She has no trouble working with one of her students who loves chemistry and has started learning about Periodic Table before entering Kinder.
On the other hand, our son's math class this year was not a good one. The teacher has no idea how to differentiate. I've talked to him directly, and even talked to the principal many times. In the end, we decided to pull him out, and he's now working independently. I teach him at home and I sometimes come to school, too, during math time. It helps that we had the SCAT and WISC-IV test results when we talked to the principal. He's also been supportive and found a middle school teacher to mentor our son in science.
The next challenge will be when our son gets to middle school next year. We've started the conversation with the principal, middle school math specialist, and home teacher about math progression. Our local public high school's principal is against math acceleration. There is a fear of 'holes' in their math abilities and of course, "We're running of math class to offer!"
In dealing with public school, knowing the laws certainly helps. You can also make stronger case when armed with results of some formal assessments. Gathering information and learning about gifted issues (esp. from the amazing board!) help us understand our children better and thus advocating for our children more effectively.
When it comes to private schools, it would be most helpful to get their stand on giftedness. I've visited supposedly highly academic private schools that are very inflexible. On the other hand, I know at least 3 private schools in the area that get giftedness and make accommodations.
