But that doesn't mean it's best for kids. In fact, in regards to learning, the reality – which each of us knows deep down if we're honest with ourselves – is that there is a vast range of normal readiness and ability among any given group of same-aged kids at any "grade level." Thus, you'll see kids in "4th grade" who can comprehend and enjoy books at a much higher reading level, and others who are still working to master phonics. And you'll notice a wide range in terms of those kids' abilities to understand whatever math is being taught in the "4th grade" classroom as well; in fact, some of the "high" readers might be the ones who struggle most with math! It doesn't mean there's anything wrong with any child; it just means that each is an individual whose abilities and needed pace of learning differ from that of other children and across the various academic areas of study.
Tragically, the sad reality within institutional schools – both public and private – is that the powers that be almost always insist on standardization – i.e., all kids in a certain "grade level" are taught the same things...at the same time...in the same way...at the same rate – and then slap deleterious labels onto children who don’t fit the algorithm. Of course, that doesn't mean the children are all engaged in the process (the ones who function at higher levels are bored out of their heads!) or are all learning (the ones who have slower natural rates of learning are being dragged along but still don't "get it"). But - beyond a few teachers who try to make allowances to some degree within the constraints of the system - that's just the way it is.
In contrast, though, we as homeschoolers have the freedom to break free from that in order to actually teach our children at each one's real ability level and pace - without regard to the system’s arbitrary "grade level" designations. It’s true that, because our culture has been so indoctrinated into the “grade level” mentality, you’ll see reference to it all over the place: your kids’ Great Aunt Sally will ask what “grade” they’re in every time she sees them; religious education programs sort and classify kids just as schools do; community-based sports activities divvy kids up according to “grade level.” It’s worth knowing which “grades” match your kids’ chronological ages to make your life – and theirs – easier in such situations. But you can – and should – break free of the lie when it comes to their academic growth and development.
In practical terms, that means that – even if you choose to go with a traditional (i.e., textbook-based) curriculum and use separate materials for each child – you should not simply go with one "grade level" for every subject. Instead, evaluate where each child is in terms of what he actually knows and is able to do within the scope and sequence of the curriculum you want to use - many companies provide placement tests to help in that process - and start there. If that means he's six but using a "5th grade" math book (I recently met a child for whom that would likely be true!), meet his needs. And, if that means he's 10 and needs "2nd grade" reading, meet his needs. Start from where your child really is and be diligent about making regular progress...but go at your child's pace of learning, whatever that is. The pace will, of course, vary over time because kids learn asynchronously in fits and starts, not in a straight line. But whatever it is, choose to put your child’s real needs over the arbitrary labels printed onto the spines of textbooks.
Also give serious consideration to using material that is non-graded to begin with. More and more providers of homeschool curricula have understood the fallacy of “grade level” and are, instead, producing leveled resources based on actual skill development. And still others create age-integrated unit and delight-directed studies where every child is free to demonstrate a depth of learning unconstrained by “grade level” limitations.
In the end, when you break away from artificial, school-based labels and, instead, embrace the real learning pace hard-wired into each child, they will all be just where they need to be upon high school graduation. They won't have gone through the cookie-cutter, assembly line schooling offered by the institutions; instead, they'll have been given individualized programs of study that took each one’s real needs into account in every facet of learning. As such, each child will be able to soar in his or her particular areas of giftedness while still being more than competent in other areas. They’ll also be much more emotionally healthy than their factory-schooled peers...and will come out of their educational experiences with a love for learning and a desire to continue learning throughout their lives. And isn't that what education should really be about?