A few years ago, teachers at Ellis Middle School in Austin, Minn., might have said that their top students were easy to identify: they completed their homework and handed it in on time; were rarely tardy; sat in the front of the class; wrote legibly; and jumped at the chance to do extra-credit assignments. But after poring over four years of data comparing semester grades with end-of-the-year test scores on state subject exams, the teachers at Ellis began to question whether they really knew wh