Being rich or poor has no bearing on someones ability to score highly on any standardized test. Its entirely about motivation which can be somewhat externally supplied by many factors such as parents, teachers or their peers; or it can be supplied by the person who is going to be taking the test.

In the US many public libraries having computers that are available for use by anyone and are often open till 8 or 9 at night(and many schools also allow students access to computers during their "free/study" period(s)). And with the Labor laws restricting the hours a minor can work on a school day; only situations at home that require their presence would prevent a self-motivated "poor" student from studying for this test.

Now how a "poor" student would be able to afford to take this test much less the crazy expensive colleges/universities in the US is an entirely different matter.