> positive correlation between family income and testing scores Correlation != causation. One of the best SAT prep available today is https://www.khanacademy.

> positive correlation between family income and testing scores Correlation != causation. One of the best SAT prep available today is https://www.khanacademy.org/test-prep/sat https://www.khanacademy.org/test-prep/sat and that is free for everyone. Standardized tests are important, otherwise students are not evaluated using a uniform criteria. GPAs can be compared only within the same school district. Even the curriculum is not standardized across states. See https://en.wikipedia.org/wiki/Common_Core_implementation_by_state https://en.wikipedia.org/wiki/Common_Core_implementation_by_...