For better or for worse, when I was in school in the 80s and early 90s, tracking started in about 4th grade (not counting kids who skipped earlier grades entirely). I essentially had about 90% the same kids in all my classes from 4th grade through high school graduation (not counting the influx from other feeder schools that joined in 6th & 9th). The result was less distraction in the classroom because everyone wanted to be there and was focused on learning, and much tighter rapport among the classmates. A lot of people make their best friends in college, but in my case, the friend groups that sustained frequently began in elementary and middle school!
The downside to early tracking is that it becomes increasingly difficult for kids on remedial and standard tracks to break into G&T/advanced classes with each successive year, but it's pretty easy to create an exception-based assessment process to facilitate these moves.
Fast forward to today, where I have three kids in three public neighborhood schools in San Jose. Math tracking starts in middle school and is based exclusively on students' NWEA (https://www.nwea.org/) scores, which determine whether you're placed in accelerated math, standard math or remedial math in 6th grade. Some schools let kids move into the accelerated track in 7th grade based on their 6th grade achievement, but many don't [because the 6th grade accelerated curriculum includes the entirety of 6th-8th grade "standard math" curricula, and expecting a kid who only received 1/3rd of that as a 6th grader to miraculously know the other 2/3rds as they start 7th grade isn't reasonable]. The result, from what I can tell, is that you have all kinds of mixed grade classes in high school now, since kids of essentially any grade could be taking the same classes (whether AP classes or core curriculum, or even electives). It's frankly a mess, and the level of distraction is off the charts. Overall, achievement of G&T students is lower and the kids at the lower end are suffering, too, because they're also not receiving differentiated instruction at the level they often need.
In my opinion, it's a great illustration of how DEI policies applied to public education can fail all student demographics. On the plus side, ironically, the social/emotional maturity of kids these days far exceeds generations past.