Answer and explanation:
The main sentence is false. The SAT was NOT made to demonstrate children's fitness from public schools. Instead, the real reason was to maintain an objective standard test to allow mainly young people from any social, cultural or economic status, that wanted to enter to college, to prove that they had the mathematical, writing and reading skills as a realistic requirement to get in (and not the social status, for instance).
Along the years, the private organization (College Board) that makes the exams have improved their tests in order to make them reliable so everybody could be able to answer them successfully, without any social or cultural reference in their questions. But, this is not always achieved, so universities sometimes ask for SAT and other alternative tests to admit students.
The problem is that the cost of this kind of tests are not cheap. Only SAT costs between 50USD and 100USD, that is not an inclusive price for people of all cultural, social and economic status. The irony here is that even if the purpose of the exam is that everybody could prove their skills to get to college regardless their acquisition, they have to pay a significant amount to prove this.