That's not necessarily the reason. OP probably was letting faster kids jump ahead but that doesn't really do anything helpful for a class that's going through a topic together step by step.
Better would have been to let the faster person learn something else tangentially related to the course so that they stay engaged but they don't disengage because they're simply ahead of the rest of the class on the next topic - which is just frustrating for everybody.
Alternatives exist for self-directed study and the tutorial system but that's presumably not what they're building for.
Or just...not have students at wildly different levels in the same class.
At high school and more so in universities, there are distinct classes at different levels, and prerequisites for those classes, and students at different levels. Bring that system to all grades, rather than just having "age N = grade X" as one giant class with pressure for uniformity.
> let the faster person learn something else tangentially related
If content someday emphasizes science as a richly interwoven tapestry, and heavily leverages implicit curriculum, this might become straightforward. The chemistry problem, that's also implicitly teaching cellular biology and supply chain dynamics, enables tangents on those too. The K-2 intro mittens, with tangents on thermal budgets, and spacesuit dexterity limitations, and winter camping clothing 101, and knitting how to, and so much more.
If OP regrets our handling of current curriculum, there's seemingly an enormous additional level of despair available, in education's profoundly impoverished opaque window into the beauty of the world.
Better would have been to let the faster person learn something else tangentially related to the course so that they stay engaged but they don't disengage because they're simply ahead of the rest of the class on the next topic - which is just frustrating for everybody.
Alternatives exist for self-directed study and the tutorial system but that's presumably not what they're building for.