How old are your kids?
Because while this sounds great (in theory), I've met very few teachers who can pull it off effectively. And as a parent to two very bright, very wiggly boys who would ... find ways to entertain themselves when they got bored ... I'm here to tell you that when this was NOT being pulled off effectively I received a number of phone calls from the school. Which basically were "Your kid was misbehaving because he was bored and unengaged."
Also, you can only do it for so long. At some point, some kids will be doing algebra and some will still be working on adding fractions, or learning multiplication. And this will bleed into science ("why is this class moving so slowly?" and social studies, and ...)
Some of our middle school teachers made this claim ("studies show..."), but the only research I could find from the past two decades showed that doing this grouping in a single Language Arts class in (Tennessee? Louisiana? I forget, someplace in the southeast) produced results for the advanced kids that were no worse then having them read quietly by themselves in the library. Not exactly a ringing endorsement. (Also, the research paper -- which I don't recall being peer-reviewed -- used an inappropriate standardized test as the metric, because it was basically someone's thesis and they presumably didn't have any $ to test the kids using something more appropriate.) Some jack-hole from the education school here convinced the middle school teachers that teaching more mixed-ability classes was more "equitable", but in practice the teachers weren't good enough or invested enough to do the work to make the whole thing effective. The two years we were involved in this were a shit-show, and our kid basically didn't learn anything in his LA class for those years.
No, I'm not bitter about my personal experience, why do you ask? :^)
My kids are 6 and 12.
So, kid #1 is in 7th grade now (out of elementary). He's a GATE kid and we kept him in our school even though we could have transferred to a dedicated GATE program.
In his class, we had a reasonably high % of GATE kids (10%), plus at least another 10-20% of kids who were high performers.
So, he was bored in kindergarten (because he'd had 2 years of preschool). His first grade teacher was FANTASTIC at giving him extra work to keep him engaged. My second kid didn't get her and she's retiring. Bummer. She just about started him on multiplication at the end of first grade but held off. He moved on to common core math in second grade, which meant he was fairly well challenged to learn the "whys" because before that...when asked how to explain the answer he'd say "I just know".
The teachers were able to adjust to his abilities BECAUSE they all worked together - so like I said, the individual grouping would take the high ELA kids from all three 3rd grade classes and they would study together during ELA time. This continued through sixth. Now, that doesn't mean there weren't challenges - we did have a couple of children who were unable to remain engaged - though they weren't necessarily "bright" kids or "not bright" kids - there didn't seem to be a relationship.
In any event, he's in junior high now, and of course, junior high divides up kids by their abilities. So he's in math compaction, honors ELA/ social studies, and honors science. The thing that I really like about his school is that they aim for mastery at all levels. So if you don't get a concept, you redo it until you do. From an ELA/ reading standpoint, everyone needs a certain number of "AR" points. But the # of points depends on the reading level of the kid. My kid and 1 or 2 others are reading at college level, so they are required to read more and more advanced books than the rest. So: not bored.
Kid #2 is in first grade. His teachers, so far, are adjusting to his level. His homework is harder and different from other kids. They already split kids out in the three classes into different reading groups. (Luckily, all 3 classes are 17-18 students this year). He's reading at a 2.8 and his math is at a 2.4. Clearly, the combination of group pull-outs, online studies (a reading and a math program), and parents and teachers who had him 2nd grade books is working.
(Also, I think schools have to adjust - our school has historically been an UMC school, but that has changed in the last 10-15 years. It took a lot of work to "adjust" to a higher % of students who were poor and English learners. You need different methods and techniques when you have a wide disparity like that.
On a more personal note, I was lucky to have teachers to do this for me too. Sadly, I changed schools in high school, and was unable to get into the most advanced math class because of how they had their schedules. I was bored silly in trig and spent most of my time teaching the other students (the teacher was the football coach, he sucked). Turns out when we turned in the book at the end of the FULL YEAR, it was designed for a semester, and we never finished it.