That is – the hypothesis that teachers significantly improve their students’ test results if they tailor their approaches to the students’ current level, learning style, or other student characteristic, vs. generically teaching according to the scripted lesson plan for that time unit. This is a fundamental principle behind remedial tutoring and special education.
Trivially, we can ensure every student receives the same education by providing a robotic teacher lecture, and dictating a set of interactions and cycle around to each student. For many special education students (especially at younger ages), we know this will not work for them. The situation for poor kids or supposedly weak learners is less clear, for reasons that include: incorrect tracking practices that don’t match up to the actual maximum potential of children (usually under-challenging); and social promotion, which allows much of the signal of over-acceleration symptoms, to be lost. Hence, most people accept the special accommodations (IEPs) of special education students, while the tracking debate remains murky other than that the average curriculum needs to be more challenging.
At the same time, it seems that the brightest/most-supported/best-parent students significantly benefit from the most rigorous instruction. So, in order to maximize their academic potential, the standard must at least be set at their level, if there is only one level of rigor available. In this regard, the cost of education and the rigor all would be equal for every student (with the exception of special education students).
Next the question comes: can you force the average or below-average intelligence students to go through 3-4 hours of homework a night, to barely keep up with the level of gifted students? This is not an option at younger grades for several reasons: the most important being that you will ruin eyesight. So certainly there will be different levels of actual progress.
“Common sense” would suggest that at some point, certain students’ understanding lags enough over time that they can’t make effective progress at the gifted level. In that case you would have no choice but to split off a track that is better aligned to their current situation. The question is, how will you measure e.g. the pace of that track? The best way would be to have a universal learning chart, where every child progresses up the chart, but at differing rates. Then, you could tell via testing when learning rate has dropped below an acceptable threshold.
The remediation process may involve several interventions, but as noted previously, one thing it can’t do is increase workload, since the increased workload already didn’t compensate enough for the differences in ability/preparation/etc. Hence, unless there are obvious factors like domestic violence or drug use involved that are preventing work or posing special obstacles, there’s no realistic way to recover the lost time, and so there must be a slower track, under the assumption that education time/cost spent per student should be about the same.
Hence we come to the first decision about equality: you could reduce the rigor to the level of the weakest student, but due to the economic imperatives, you won’t do that (unless you are talking about a mediocre American school, where the principal only really cares about social promotion and keeping his job). Then (in a school of a size that can accommodate multiple tracks) you must provide the down-track education, and now you have the poor kids in one track and the rich kids in another. You still could make some argument for the equality of education dollars spent at this point. If, however, you want to try to remediate or intervene in the struggling child’s life, you now are allocating more resources to the poor children than the rich.
The end result of the first approach is that the poor children simply don’t complete all the course material that the rich ones do. But what happens if you required the course material for a good reason, such as civics? Then you must spend more money and time on the poorer students, in order to get them through the remaining material that they couldn’t cover as quickly.
The other viewpoint: if school is only really about the economics, and you have a class of poorer learners for whom it likely doesn’t make sense to send them to college or advanced vocational, then why are you spending money to remediate or complete the nice to haves in education? They aren’t going to use Algebra II or Physics in their daily lives, and nothing prevents them from studying them on their own later on (and even to get subsidies or reimbursement based on merit later if they actually complete those courses). Hence it is an unjustified use of taxpayer dollars to, by default, spend money to push them into courses that are basically useless to them. But, if you say, only some classes are required, then why are we having the gifted kids forced into compulsory courses that they don’t need? If they are going to college anyway, why not just start it then?
Hence you are forced into a critical decision about required curriculum and even social order, based on your views of the benefits of tracking as well as overall schooling benefits. Moreover, if you were to try to maintain the same amount of financial contribution to education, you would have to credit the gifted students with graduating early/with fewer supports.
The situation gets even uglier when you consider why the students have the differing learning rates. It’s usually attributed to a combination of inherent ability (usually not that strong an influence) and parental involvement/education/exposing their kids to various useful words and experiences. So, in the system where the weaker track is remediated, the parents put more investment into their children and get less reimbursement from the school system for their proper efforts; an obviously negative incentive to doing the obviously right thing.
Another issue is the most effective frequency of tracking decisions, and the basis on which the tracking decision is made. Especially at lower grades, where students learn different things at different rates, the tracking could even be at the level of a week. If that decision is made informally, there is no means to distinguish tracking based on academic performance from tracking based on social factors, racism, etc. Hence in order to provide individualized instruction (presumably the best type), one must have roughly similar tests that gate each tracking decision. Practically speaking, that means that if you are a parent, and you have a book full of tracking tests, you should be able to assess your child and determine whether their current class is too easy for them; then you should be able to hand that test to the teacher/school administration and move the student to the next higher level. That could involve staying in the same class and getting different material piecemeal (effectively part-time tutoring), or it could mean advancing on the same track, or it could mean moving to a higher track, if the student’s learning rate routinely exceeds peers on the same track.