For decades, school districts have organized around a simple idea: Whatever you give to white students, give it to black students, too. Put both groups of students in the same schools. Expose them to the same teaching. If they struggle, give them the same help. In the Tampa Bay area and across the nation, this was how educators atoned for the long-ago sin of relegating black children to inferior schools. Now, in a class-action lawsuit that has Pinellas County's top educators on the defensive, the plaintiffs say the policy of equal access has failed the school district's 20,000 black students....