AUSTIN -- A new school accountability system unveiled Tuesday emphasizes how well campuses and districts close achievement gaps between minority students and those from low-income families and their white and wealthier counterparts -- but stops short of issuing letter grades as promised for next year.Since taking over as the state's top education official in August, Education Commissioner Michael Williams has been working to revamp the criteria used to rate traditional public schools, charters and school districts.Williams is scheduled to issue school and district ratings using the new system Aug. 8.They replace a previous framework that based ratings and rankings on student performance on state-mandated standardized tests.That was frequently criticized by the education community, which claimed it was all-or-nothing proposition, since poor scores in one area of exams could hurt overall ratings.The new system calls for rating schools and districts on overall student performance on standardized tests, student progress as they work their way through school, and their college-readiness upon graduation -- with the latter applying only to high schools.Williams has focused on the student achievement gap component, saying that given that Texas public school students are now "60 percent economically disadvantaged and 60 percent black or brown" the state's accountability ratings can no longer afford to ignore large and growing achievement gaps."I have heard the criticism of the previous accountability system, with its overemphasis on a school's lowest-performing areas and its blind spot to what a district or charter might be doing well," Williams said in a statement. "The new system makes use of multiple indicators to provide parents and taxpayers a more detailed overview of the successes, as well as areas of necessary improvement, for each school district, charter and campus."Still, the new rating system continues to heavily rely on student performance on the State of Texas Assessments of Academic Readiness, or STAAR exam, a standardized test which has triggered a firestorm of controversy since it was first administered last school year."Those districts and campuses that are leaders in improving achievement for all its students will be easily identified under this system," he said in Tuesday's statement.Schools and districts receiving ratings like "Exemplary" and "Academically Unacceptable," though a series of proposals in the Legislature would institute an A-through-F letter grade system, which supporters say will be easier for parents and community members to understand.Williams told a Texas Senate committee this month that he planned to unilaterally institute a letter-grade accountability scale starting in 2014 -- without waiting for legislative approval.