[generally]

I couldn't access the original article to see if it had more details, but I would offer several possible explanations.

1) Kids are getting dumber. (I don't really think this is the case. I include it for the sake of completeness and because most people, out of PC-ness, refuse to consider the most obvious explanation.)

2) Quality of education is dropping. (I strongly believe this is true.)

3) The test is too darn long and the exhaustion factor causes scores to drop. (A good possibility.)

4) Many more kids are taking the test. (Highly likely. I think far more kids are encouraged to take it than in the past. If the test used to be taken primarily by college-bound A and B students, but is now being taken by a lot of C students, then the average scores are sure to drop.)

5) The test is faulty. (Actually, I'd bet that all the test tinkering would be more likely to raise scores. They have eliminated the analogies and a lot of the tougher questions, although in some areas, I think they claim to have added a higher degree of difficulty.)

6) The change in average scores is not statistically significant. (I'd have to have a lot more data to judge this.)

[sono]

You left out the elephant in the room:

It's Bush's Fault!

[HitmanLV]

Every test is biased, but not in the way a lot of race hustlers insist.

Every test is biased in favor of those who have developed the skillset to perform well on the test.

Develop the skillset, improve results on the test.