There is no argument against academic acceleration beyond that it increases inequality of achievement. If the school system was about education more than childcare acceleration would be the norm for bright children and we’d have 14 year olds starting their Bachelor’s level studies in every school and 20 year olds who already had doctorates in every city of any size. Instead we waste their time, to their detriment and…
That's also why you practically never hear about anyone being left behind a grade. From the start of kindergarten to the end of high school, the everyone I knew who started in my grade finished in it. I can't remember a single exception. In what other areas do the fastest and slowest do 13 years of work at nearly the exact same pace? The only difference allowed seems to be in AP classes, which are pretty limited in a…
Schools are already struggling to handle incoming class sizes, they don't have the bandwidth to increase any throughput by holding older students back. To do so would be to the detriment of those incoming students and the teachers. (There's a good short scene in the Wire that sums it up but I can't find it).
The problem isn't really that students don't get held back, it's that there is no capacity in the system to handle cases where someone should be held back. Almost across the board.
I went to an affluent public school in the suburbs of a major city, and their solution wasn't to hold kids back. It was to differentiate enough between accelerated and decelerated programs to where they could essentially shovel the poor performing kids into a bucket where they wouldn't bother too many teachers or other students.
I don't know the ethics of that. A lot of those kids I knew wound up dead from opiates, in jail, or still at home.