Standardized test scores.

For his Statistics class experiment, researcher J.Gilbert decided to study how parent's income affects children's performance on standardized tests like the SAT. He proposed to collect information from a random example of test takers and examine the relationship between parental income and SAT score.

a) Is this an experiment? If not, what kind of study is it?

b) If there is relationship between parental income and SAT score, why can't we bring to a close that differences in score are caused by differences in parental income?