One small problem with school grades:They're a sham.All of the money, all of the time, all of the kvetching surrounding Jeb Bush's school grading scheme is utterly worthless because the proper context is rarely considered.What do I mean by that?The single most predictive factor in a school's grade is the poverty level of the student body. You tell me how many students are eligible for the free/reduced lunch program, and I can usually tell you a school's grade.For instance, since 2011 there have been 71 grades handed to Pinellas County schools that had 30 percent or less of the student body in the free lunch program. Those schools have had a combined grade point average of 3.84. Pretty darn good.On the other hand, there have been 122 grades given to Pinellas schools that had a 70 percent or higher enrollment in the lunch program. The combined grade point average in those circumstances was 1.62. Pretty darn bad.All of the schools in between? A 2.97 GPA. Pretty average.I'm no statistician, but I believe that's called a trend.We can argue the reasons why wealth plays such a large role, but we cannot deny its impact. Any bar graph of school grades would show a perfectly symmetrical line beginning with schools in rich neighborhoods and trending relentlessly lower as you travel down the economic ladder.And yet the blockheads we send to Tallahassee refuse to acknowledge this.Instead of working on real solutions for the economic/education gap, legislators have declared war on the principals and teachers unfortunate enough to work at high poverty schools.If students score low enough on standardized tests, it triggers a mandatory turnaround program that can lead to employee upheaval.Which brings us to Dunedin Elementary.This was once a highly regarded school with the test scores to prove it. Back in 2005, Dunedin scored a coveted A in the state grading system. At the time, its free/reduced lunch rate was 53 percent. As that rate increased to 59, 62, 63 and then 67 percent, Dunedin clung to a B grade. By 2010, the rate was up to 78 percent and Dunedin dropped to a C. By 2012, it was 83 and the school was down to a D.In 2013, the school fell to an F and was destined for turnaround status.So the principal was demoted and more than a dozen teachers were jettisoned. Pinellas superintendent Mike Grego says the F grade required him to begin a turnaround process, but he said many other factors contributed to the staffing changes."It's not all about a single letter grade,'' Grego said. "It's how things are moving forward, and the leadership dynamics. It's my job to look at the best interests of the school, and what can be done to move it back to being an outstanding performer.''Grego likened it to a struggling baseball team that changes managers simply to provide a new voice.With that in mind, he made his decision before the 2013-14 school grades were released. It would be disastrous, he said, to wait until summer to make widespread changes.Editor's note: This column has been edited to remove an incorrect number found in state records. It is estimated that 83 percent of students at Dunedin Elementary in the 2013-14 school year were from low-income families that qualified for free and reduced-price lunches. An incorrect percentage initially was reported.