The decline has led some commentators to embrace demographic determinism — the idea that the verbal scores of disadvantaged students will not significantly rise until we overcome poverty. But that explanation does not account for the huge drop in verbal scores across socioeconomic groups in the 1970s.
The most credible analyses have shown that the chief causes were not demographics or TV watching, but vast curricular changes, especially in the critical early grades. In the decades before the Great Verbal Decline, a content-rich elementary school experience evolved into a content-light, skills-based, test-centered approach.
Daniel Willingham on this subject:
More: How Knowledge Helps - It Speeds and Strengthens Reading Comprehension, Learning—and Thinking (Cross-posted at Cost of College)