Florida school grades are due by late July, but their validity will be in serious doubt this year.A divided state Board of Education voted Tuesday to prevent the grades from dropping more than one letter at any school, marking the second straight year the board padded grades. The change brought sharp criticism from some of the very people who helped create the state's accountability system a decade and a half ago. Many publicly questioned whether the grades at the center of that system still had any meaning.Of the 262 schools slated to earn an F this year, just 108 will get that grade now, board member Sally Bradshaw said.In a 4-3 vote, the board adopted Education Commissioner Tony Bennett's recommendation to maintain a "safety net" for schools as the state imposes higher academic standards within the next few years. Bennett proposed the change after several superintendents complained that low grades projected this year at many schools would not accurately reflect student performance.But debate among board members raised significant questions about whether the A-F grading model, which has been copied in several states, has become invalid in its 14 years. "We've overcomplicated the model," said veteran board member Kathleen Shanahan, once the chief of staff for former Gov. Jeb Bush, who is widely considered the author of Florida's school grading system. "I am struggling with the integrity of the accountability system . . . and the reliability of the grades."Said Bradshaw: "I don't understand when it became acceptable to disguise and manipulate the truth simply because the truth is uncomfortable."Even board Chairman Gary Chartrand, who voted to pad the grades, harbored doubts. "I don't think the truth is being revealed in the current grading system," he said, adding that he trusted Bennett to fix the problem.In the early years, school grades were controversial but simple, giving the public an easy gauge of school success.The grades quickly became prominent in school vernacular. School board members and elected superintendents touted them in campaigns. Residents used them when buying and selling homes. Mayors gave out awards based on school grades.Principals at highly rated schools celebrated their successes, while those at low performers looked for ways to improve. In both cases, the leaders looked less at the actual grades than the data behind them, which revealed where instruction needed attention.In time, the system changed to reflect nuances in the results. Bennett said it had become "overly nuanced" in the past 30 months, with the state inserting new calculations "to account for specific situations."Concerns over such manipulations arose in 2012, when the state board lowered the passing score for the FCAT writing exam to avoid a dip in grades. Board members said the changes were temporary, aimed at helping schools adjust to new standards.This year, as superintendents continued to warn that grades would drop because of machinations with the formula, board members called for a review. That led to Bennett's "safety net" on school grades and the debate over whether it harmed the system's validity.Bradshaw argued the model had grown heavy with politics, straying from its mission of monitoring whether students are doing well on the FCAT. She argued the state would not condone padding students' report card grades and suggested that doing so for schools did more to bolster the self-esteem of adults than to make schools better."How could we in good conscience let an F school become a C or a D?" she asked, adding the change could prevent assistance from getting to schools that need it. "The truth will lead to better schools in the long run."Bennett, who implemented a similar program while Indiana's education chief, stressed that he firmly supported providing adequate information to parents and others who want to know how schools are performing."I think we will have to make sure that everyone understands true school performance," he said. "The data will speak for itself."He rejected the idea of lowering the bar now, saying students and teachers must be prepared for the more rigorous Common Core State Standards and their associated tests. And he swatted aside Shanahan's suggestion that the state not issue grades for a year while it sorts things out."I believe as a purist on accountability that taking a break from accountability is very simply bad policy," he said. "It sends the wrong message."State law also requires school grades every year.Bennett said he considered the safety net a reasonable compromise that would cushion the state's transition to its next accountability system. He said he would not recommend it continue beyond that point.Staff writer Cara Fitzpatrick contributed to this report.