What alternative do you propose? Additionally, how will this be balanced with other facets of the person that may not be on the same level as a child's capacity for learning, such as social skills or emotional discipline? How might pushing some people through the education system faster influence society more broadly in terms of socioeconomic status and labor laws? There are many of nuances to consider here before ditching the idea of grouping children by age in the education system, I think.
There are a lot of things to consider, but there are also a bunch of things schools can do to improve in this area without having to physically move kids into different years.
Again, my focus is primary, so I accept there are differences in secondary in terms of structure. But in Australia, most schools have mixed age groupings already. This isn't done on the basis of academic ability, they are just literally mixed age groupings. So rather than being a Grade 4 teacher, I was a grade 3/4 teacher, and I had kids from both those years in my class.
My comment would be that on the whole, the mixed grouping caused no issues. If the ages were more diverse, then I can see that it might. But this is a vastly different scenario to the one where you take the smart kid and skip them through year levels (or take the slow one and hold them back). It doesn't isolate kids of a certain age.
I think it's also vital that lesson planning considers what to do with the kids capable of completing the tasks given quickly. There are a couple of things I mean in this.
1) Don't give them the same task. Give them a similar task. Again, isolating a single kid is not what I mean here. When I was teaching maths, I would choose a topic (let's say multiplication) and teach multiple aspects of multiplication in the same lesson. It took some organisation, but it worked astoundingly well. Rather than getting kids to do 20 problems, I was getting kids to do about 6 which were pitched somewhere along a continuum. The idea is that everyone was working on multiplication, but (hopefully) at the level that was achievable to them, but only just achievable (ie. challenging).
2) Have ongoing projects which are of interest to the kids. Don't ever have them doing 'busy work' designed to keep them out of your hair. Have them doing open-ended tasks, and push them to complete them at the highest level they can.
Someone mentioned IPPs earlier, and whether these are formally written up or not, good teachers should ALWAYS be considering the individual students, their capacity and their needs.
Organizing kids based on social ability and academic ability is probably ideal, but there are issues to consider. However, the goal of setting them tasks and challenges which are in no way based on the 'norms' of their age grouping is perhaps more easily attainable.
I ask these questions part because I was one of those kids who
could have skipped a couple of grades. My parents decided not to do this because my capacity for learning simply wasn't in the same place as other aspects of my person. Instead, I was encouraged to participate in extended learning programs and after school activities that provided me with additional opportunities. It seems that these kinds of programs are a good compromise, though I hear that many of them have been cut since my tenure in the K-12 system.
My sister and I were looked at for...I dunno...accelerated schooling, I suppose, but in different ways. Our primary school wanted to skip my sister ahead a year, and only the social aspects held them back from doing that. I don't think (but can never be sure) that it would have helped her much.
When I got to the end of primary, I was offered a scholrship in an accelerated high school program that would have have me graduate high school in 4 years. My parents turned it down for social reasons. I wish they hadn't. I smashed high school for a couple of years, was bored stupid, developed bad habits, and slid through. An easy way for me to fit in and conform was not to be TOO smart, and the school I ended up going to was not academically strong. Being around other 'smart' kids would have meant I'd try to conform by being as 'smart' as I could...
When I reached Uni, I ended up being good friends with a girl who did extremely well at high school, but had chosen to do teaching anyways. Her work habits rubbed off to some degree (I was never a studier, but at least I took the work seriously) and we both ended up with Honours.
My point is that smart kids work out clever ways NOT to stand out sometimes, but that happens when they are in their own year level as well, not just when 'accelerated'.