From the sound of things, it seems like the focus has shifted from allowing everyone to work at their own level with those who are in average and remedial groups getting additional help to slowing down the accelerated learners so that the others aren’t outpaced. It used to be that slowing things down would cause the advanced learners to get “bored.”
It’s just as important to not hold the accelerated learner back as it is to uplift the students who may need extra help or are falling behind.

I also taught grades 4 – 6 for 35 years and have much experience with differentiated instruction. Two techniques that I found most useful were:
Peer Tutoring: It helps the weaker student learn the material and the stronger student to review it, along with learning social responsibility skills.
Extra Credit: Who says 100% needs to be the highest score? So I challenged the students to attempt all sorts of problems, including some that hadn’t even been introduced. If they got it right, they got extra credit that would improve their overall score because there was no upper limit. (If they got an extra credit problem wrong, it didn’t count against them.) That helped weaker students to get C’s and B’s, for which they were thrilled. The strongest students competed to see who would come out with the highest percentage score (generally something like 160%). So there were lots of A’s, needless to say. AND their standardized test scores far exceeded my students’ demographic.

Instead, they followed the approach of many other districts in Westchester County. In sixth grade, there became two tracts – “regular” sixth grade math and enriched math. Both of my boys were placed in enriched math, which follows the same curriculum, but provided them with more project-based, real life problems for kids to work through.

In seventh grade, kids could place into the accelerated math program, which would culminate in kids taking algebra in 8th grade. In order to get into the accelerated math program, kids would need to have a 93 or above in the second and third quarter grades, score at least a 90 on the midterm exam, and score higher than 90% of all students on the STAR tests in the fall and winter. In addition, kids who wanted to get into the accelerated math program would have to take a math placement test given by the 8th grade teachers. There was no parent input and no racism, as grades and test scores are concrete and provide a clear indication as to whether or not, students could perform at a high enough level to do well in an accelerated program.

On a side note, my kids would complain a lot about being bored in middle school and elementary school. They would finish their work really early, and would have nothing to do for the last 20 minutes of class. They would also complain of teachers explaining things too many times, and not allowing them to do the work. They received straight-As throughout middle school and into this year. Some students really need more challenging programs. And this is despite the school being #56 in New York State.