Murray says on page 21 in his book Real Education:
"This point needs emphasizing. Educational measures such as test scores and grades tend to make differences among schoolchildren look as through they are ones of degree when in reality some of them are differences in kind. For example, a timed math test limited to problems of addition and subtraction, administered to a random cross-section of fourth-graders, yield scores that place children along a continuum distrubuted in a shape resembling a bell curve. Those scores appropriately reflect differences in degree: Some fourth-graders can add and subtract faster and more accurately than others, but they are all doing the same thing and almost all children can be taught to add and subtract to some degree. The same is not true of calculus. If all children were put on a mathematics track that took them through calculus, and then were given a test of calculus problems, the resulting scores would not look like a bell curve. For a large proportion of children, the scores would not be merely low. They would be zero. Grasping calculus requires a certain level of logical-mathematical ability. Children below that level will never learn calculus, no matter how hard they study. It is a difference in kind. Not only that: The child without the logical-mathematical ability to learn calculus cannot do a wide variety of other things in mathematics that are open to teh child with the requisite level of logical-mathematical ability.Ouch. That mindset goes against all the pop psychology and all the self-help books that tell you that you can be anything you want so long as you try. If you want a college degree you can have it if you apply and attend and do the work.
The same distinction applies to linguistic ability.
Having worked with kids, my own closely through homeschooling and with some other kids, it has been just in the last three years that I have repeatedly seen examples of kids who just don't get it and may never. It pains me to say that as I formerly held the above belief about "you can be anything you want and you can do anything if you just try". The advice to "do your best" is often assumed to be linked to the result "you will then fulfill all your goals and achieve all your dreams".
I have seen kids who seem to have "the lights on but no one is home" and others who try very hard and can do work then the next day they cannot do that same thing.
Some discuss these issues in light of learning disabilities where uneven performance is seen: what was mastered last month is absent from the memory this month, the multiplication fact that was memorized two years ago and used cannot be recalled today. If you read about these issues you may see references to things such as "executive function" and "working memory" and "recall". Things get complicated when LDs are discussed because at some point some people just cannot be cured or fixed, so their performance impedes their progress at achieving a goal such as learning vast quantities of academic material or even if learning is achieved, the student may be a "poor test taker" who cannot spew out correct answers at a fast enough speed. Thus their low test scores impede both class grades and standardized test scores which snowball into the fact that low scores may prevent a student's access to higher level courses in school that are college pre-requistes or the low grades or SAT scores may prevent them from being admitted to some colleges or to seek certain majors.
Perhaps not getting in to the college of one's dreams is okay though as just college admission is not good enough, the college student must be able to do the work of that college. To state it another way, the issue is not just how to get in to college the issue is that the admissions process is set up so as to try to allow in only those students who are capable of handling the academic workload of that college. The true issue is when a student wants to have a degree from a certain college but can't do the work to get it. That is not unlike people who say they want to be the author of a published book but are unwilling to actually do the work that writing a book requires!
We have seen the college competency issue in two types of examples. Sadly I have heard that some poorly educated poverty level minorities with hopes for achieving the American Dream that includes a college degree be taken advantage of with having taken out large student loans to pay for tuition, then unable to hack the academic coursework, drop out leaving them with the loan to repay. Regarding the recent high school graduates, we see kids who need five or six years to complete a four year degree since they need so many high school level remedial courses at college before their 'real' college coursework can begin. For some, the only real issue is the one or two years of extra tuition that the student or parents wind up paying.
This whole discussion would be considered controversial by some, the idea that kids are different and another of Murray's beliefs discussed in this same book, that "ability varies".
When I think about these issues I usually am left feeling sad that every person can't and won't be a scholar and frustrated by the so-common advice of "you can be anything you want" when in fact it just is not true.
Murray wants education reform. Public school reform in America has been attempted in the last 110 years when it really began about 160 years ago, thus the system made it only about 50 years before there was serious criticism of it. It doesn't seem to me that real reform has been accomplished at all.
I guess really all that matters to me, if I boil it down, regarding that philosophical discussion of "ability varies" and "a difference in kind" is how those issues affect my own life and the lives of my children. I, as an individual, am powerless to "save the world" or "help all children" or to try to reform American public schools but I can have a major influence over the education of my own kids. That is why we are homeschooling. The trick though, is to deliver a high quality home education while also meeting the legal requirements of the government (which varies depending on what state one lives in). Also, since my kids have aims to enter college, I need to get our ducks in a row to have my kid's education be the right type of college preparatory program that they need to do what it is they think they want to do for their career.