There is only a moderate correlation between income and taking of test prep
Under-performing minorities are more likely to take test prep than whites
In other words, quite a few people taking test prep are ones likely to be going to poor, under-performing school systems. Either test prep companies are incompetent or our school system is doing a lot better than I had expected, even on the low end!
While a good point, the OP’s link says that:
There is only a moderate correlation between income and taking of test prep
Under-performing minorities are more likely to take test prep than whites
In other words, quite a few people taking test prep are ones likely to be going to poor, under-performing school systems. Either test prep companies are incompetent or our school system is doing a lot better than I had expected, even on the low end!