I don’t think this is usually not about “lowering” or “raising” any level, and I think this is a slightly different issue than the typical “do you teach to the strong or weak students?” The problem often arises when schools/ parents push ahead to get to the “next” step faster. This can be almost impossible for slower students, but it is not necessarily better for stronger students either. Putting more knowledge into your brain is usually not the best way to use it, and rushing to the next step may prevent even the stronger students from getting the most out of that stage.
A recent study comparing the science textbooks and curriculum used in various countries found that countries that produced students who did better in science generally had a curriculum that covered less topics per year, but spent much more time on each topic. Students taught like that were found to develop better understanding of the concepts rather than the facts, to retain the information longer, and to be more able to apply it to other situations. Lehavdil there are some similarities to the Zilberman model.
The point is not to go “slowly” and simply repeat everything numerous times (which would obviously be unfair to large numbers of students). The point is to build skills and knowledge in a systematic and developmentally appropriate way.
truth be told — I have worked in education for many years and have yet to find the student who becomes a real behavior problem simply because they are too bright and suffer from boredom. Actually my experience has been that weaker students, especially those with disabilities are the most likely to exhibit behavioral problems. In my experience the only students who act out from boredom are those who either require a lot of stimulation (i.e. they are bored from the style of the class, not as a result of the content being too easy), or have ADHD type of attentional or impulse control issues (seen in areas other than academics as well).
I’m not saying bright students are not bored — they often are, and I believe a teacher has as much of a responsibility towards the top students as towards the weaker ones. I am simply addressing what I think is the myth that the “boredom” of being “too smart” leads to behavioral issues. I would love to hear what other educators have observed.