A special tabulation of individual student scores from the Texas Assessment of Academic Skills (TAAS) test allowed a ranking of Texas schools according to test score changes ("value added"). The rankings varied greatly by student subpopulation. That is, the vast majority of schools are much more effective with some kinds of students than others. The implied comparative advantages suggest possibly large academic gains just from indicated student movement, even among unchanged, traditional, "comprehensively uniform" public schools, perhaps through well-informed public school choice. Further gains from specialization are also implied by the results. (Contains 6 notes, 2 tables and 1 figure.)