It’s hard to give an average figure for how much test “prep” or “coaching” increases scores because that entirely depends on your definition of “prep” or “coaching,” and which groups we’re studying. So organizations can manipulate findings to find literally whatever they want to by selecting the right group of students and asking about the right kind of prep. Are we talking about students who are already scoring in the 700s in each section, or students in the 500s who have more room to improve? Are we talking about students prepping on their own every Saturday for two hours over two months or students in a structured intense SAT class taught by a national provider - or, even better, those with private at-home tutoring? Are we talking about students who are struggling to learn English as a second language or students who grew up with two PhD-educated parents? Are we talking about sudens who have to work a fast-food job to help feed their siblings or kids who drive a BMW to their boarding school?
FairTest (who has a vested interest in showing that coaching raises SAT scores a lot) cites an average score gain of 60-75 points on the M section from a 2001 study. College Board (who has a vested interest in showing that coaching hardly matters) says average overall gains are only 15-20 points on verbal or 20-30 points on math. A 1999 study showed only modest increases…but the survey was sponsored by the College Board.
It really depends on how they conduct the study, and few of these non-scholarly sources are actually operationalizing “test prep” and reporting what they mean by that. (FairTest does describe the study’s; it included 30-35 hours of test preparation taught by someone else, with at least one practice test built in.)
There are many theories about this. One of the most prominent is academic disengagement as a protective mechanism. Historically and culturally, African Americans were barred entry from most bastions of higher learning either by law/policy or by reality (financial reasons, undepreparation, etc.) It’s only relatively recently that black students have better opportunities to access good educations.
One theory is that a protective mechanism that all humans engage in is that when something is prohibited to you, you act like you don’t want it to avoid emotional pain. Kind of like sour grapes. So the disparaging of education (allegedly) is a manifestation of that. Another theory is that it’s a simple reflection of what we see. When your entire culture’s higher-educated population is white, then attaining an education and being serious about school does quite literally mean “acting white” - in other words, making changes to yourself to fit in with the mainstream culture, so as not to be threatening or othered.
I’ve reflected on this a lot in my journey through college, grad school, and my current job. One minor example is that my voice sounds completely different among friends than at work/school. It’s an unconscious effort to fit in and sound more “normal” or “professional” (which usually keys into “white”, and specifically “Middle America white”), and one that has been honed over several years of practice and learning through consequences. In fact, I once gave an interview about this. The interviewer asked me to give her an example of the dialect I speak with my friends and family, and I was completely unable to come up with an authentic example in the moment because the switching is so automatic and unconscious for me AND because over time you become so averse to (and fearful of, and vigilant towards) “slipping up” and using the wrong dialect in a professional situation to a white person.
That’s just one example. Another is that when I was a grad student instructor, I had lots of young black female undergrads very anxiously ask me if their naturally textured hair was something to worry about, about my experiences interviewing with natural hair, and whether they should straighten it so they could get jobs. It’s like such a ridiculous thing - this is the way my hair grows out of my head, I shouldn’t have to alter it to get a job - but there’s a perception among some employers that naturally Afro-textured hair (or braids, or locs) are “unprofessional” or “militant”.
To succeed in mostly white environs (which generally get whiter as you go higher) like higher education and top-ranked jobs, there are adjustments to your cultural mannerisms you must make. You have to adopt a value system that’s not really part of your frame of reference growing up, and you have to learn how to move fluidly in that. To a certain extent, that’s true for everyone - true for the rural Midwestern white kid who moves to New York to work Wall Street, too. It’s just…life. But the differences are more profound for minority group members (not just racial). And they are stressful! There’s research on that, too - how stressful and how much mental energy it takes to maintain the image that you are an acceptable in-group member worthy of the job/education/whatever.
And some kids understandably resent that. Or it’s too difficult or stressful for them to do the code switching, so they rebel and push back. Unfortunately, that “pushing back” is often against something that will help the excel socially and economically.
However, I do want to add that there’s a lot of research disputing the ‘acting white’ hypothesis. I’m not saying that some students don’t experience it, but there’s a lot of evidence that this is not as widespread or ubiquitous as people think it is. My middle and high school were 98% black and I was never once accused of “acting white” despite being one of the top students in my class. On the contrary, my achievements were celebrated by peers. Being smart and going to college were very much positive things. A lot of studies of high-achieving black middle and high schoolers actually show that they have pretty high self-esteem and achievement goals, and don’t feel like their blackness is at odds with their intelligence and aptitude. Other studies suggest that black students, on average, are no more alienated from school or achievement than white students and don’t incur any more penalties from peers for high academic achievement than white students do.