Educators are excited about new national S.A.T. averages for high school seniors, released today, that top all since the early 1970s. ButTIME's Richard Ostlingreports that analysts are cautious: "It is only about a 3 percent jump, which could just be a statistical fluke." One likely explanation: the two leading test prep courses, Stanley Kaplan and The Princeton Review, report enrollment increases of 10 percent, and test prep book sales are up 25 percent. The results also may exacerbate the "Bell Curve" debate over black student performance, Ostling adds: "The relatively poor showing for blacks raises again the nature versus nurture argument."