I'm too tired to write much, but I personally feel that if a child has completed a year of a math curriculum and is proficient in it, spending another year repeating the same curriculum in "more depth" is a waste of their time. They already know the material. The VP at DS6's school used the same line with us, but we did end up getting DS and the one other 1st grader who took 1st grade math last year into 2nd grade math this year. It was a logical continuation for them.
Is there any way your school would be willing to make an exception to their "we don't accelerate, we differentiate" rule for new children who have truly already had the entire year's math curriculum? I can understand differentiating if they hadn't already learned all the information, but really, how much deeper can one go in 2nd grade math? If they're not figuring out how to differentiate and won't accelerate, I'd think that some independent learning would be better than sitting through the same material again. Others here have more BTDT experience with older children and might have some better advice and more specific resources about independent learning than my tired brain at the moment.
