o be direct and normative philosophy aside, it is all about students who obtain high marks and those who do not.
The meaning and implications of the tern "Low Achievers" depend on how you look at it. What is for sure is that "Low Achievers" are allocated to the opposite side of the "high achievers" in the classroom grade Bell Curve (Normal curve) . The decision on exactly what percentage 'should be' considered as low achievers depends on the criterion you yourself set to "Average achievers". Low achievers are on the left side of the curve. Is this 'arbitrary', non-sense and even damaging? Yes, it is.
I think you mean to help those in the class who get lower grades. You might want to take a look at the meta-analysis works reported in the book " Visible Learning" by John Hattie. What I find interesting in this work is even in simple activities such as summer camp, high achievers get significantly more than low achievers. (Hey, by the way, nobody likes tagging people with any kinds of low or high adjectives. I never do that, not even as a joke)
So, here, the Matthew effect (or accumulated advantage) "the rich get richer and the poor get poorer" that sociologists use as a descriptive tool actually happens. What it suggests to me is the following. Not "learning disabilities" but " learning difficulties" seem to be real. I think here (Zone of proximal development to use Vygotsky), the mission of teachers should be.