Why do you put stock in standardized test scores?
Do you have any evidence that one shouldn't? I'm not here to do your homework for you, but a few things that come to mind are proven positive correlation with lifetime earning ability and state measures of wealth and income, negative correlation with prison population percentages by state, and a recent history of improvement in the SAT tests themselves.
The latter is significant, during the 80s and 90s the SATs actually were made less difficult because top schools were not seeing the high scores they once did and did not want to lower their visible thresholds for admission so they successfully applied pressure to the Educational Testing Service to tweak the numbers upwards. In the last decade increasing complaints from all schools about the reduced screening effectiveness of the test led to a restructuring of the tests, for example, testing writing abilities.
Considering the period when the SATs were "dumbed down" so Harvard and others could look good, the 40 year decline in performance described in the articles above is actually worse than the score data would indicate. One might also wonder how much denialism about the validity of the tests impacted student performance, if Joe Know-Nothing's kids picked up the message that they didn't need to perform on no steenking SAT tests because the tests were not meaningful, pressure to perform in the areas the tests measure may have been removed.
You're on an incorrect thread of causality. Success on the SATs has virtually nothing to do with intelligence; it's about half information regurgitation and half test-taking skills. Scores have declined over the years because a fair portion of the public has realized that standardized tests are no measure of future success and has stopped treating them as such. The fact that people who do well on their SATs are more likely to succeed is irrelevant; simply doing well on the SAT has a significant effect on college admissions, scholarships, and the like - enough to skew percentages that the ETS will no doubt use to persuade people of the validity of its test. I'm not disagreeing with the claim that education in the States is getting worse - nor am I agreeing with it - but in any case SAT scores are no valid proof of anything except the willingness of the public to accept far too much at face value.
Tl/dr: One guy thinks SAT scores mean something with regards to ability to get shit done and contribute to society, others question this idea.
1) Perhaps SAT measures nothing more than literacy, but because college admissions uses the scores as a metric, the people who score high get to go to uni and meet people from wealthy families thus putting them on track to be wealthier, etc. This could occur regardless of what SAT measures.
2) How are these state-wide and nationwide scores calculated? Has the number of students taking the test gone up in certain populations of people who may have various reasons to score low? Perhaps as the test became more popular more and more schools began administering it. At a certain point only the lowest common denominator schools are left to join in.