High-school students' performance last year on the SAT college-entrance exam fell slightly, and the score gap generally widened between lower-performing minority groups and white and Asian-American students, raising questions about the effectiveness of national education reform efforts.

Average scores for the class of 2009 in critical reading dropped to 501 from 502, in writing to 493 from 494 and held steady in math, at 515. The combined scores are the lowest this decade and reflect stalled performance over the past three...