Hillsborough County School District leaders are praising students and staff for improved grades in more than a dozen historically low-performing schools.

The district announced Tuesday that out of 28 schools in what it calls its “Transformation” group, 14 are positioned to improve their state letter grades from a D or F to a C or B.

Eleven of those schools are among 39 on a state list of “persistently low performing” schools, the most of any district in Florida. The higher grades would move them in a positive direction, district officials said, but they need at least one more year of strong performance before they can be removed from the list.

Because of the COVID-19 pandemic, the Florida Department of Education has not issued school grades since 2019. But the state is allowing districts to opt in for 2021 grades at specific schools, in a process that will take about a month. To qualify, the state says the school must have tested at least 90 percent of qualified students.

Based on the data reviewed by the Hillsborough district, these schools should qualify for C grades: Oak Park, Dunbar, Cleveland, DeSoto, Foster, Kimbell, Potter, Witter, Mango, Mort, Thonotassassa and Pizzo K-8.

Two schools — Kenly Elementary and Folsom Elementary, showed improvement from a D to a B.

The grading system, launched during Gov. Jeb Bush’s administration, has evolved over the last two decades in response to complaints that it was too punitive to disadvantaged communities. The current system gives schools credit not just for test scores, but also for improvements from one year to the next. And it gives more credit for improvements shown by students in the lowest-scoring quarter.

Because the grades rely so heavily on improvement, they are not easy to maintain, and superintendent Addison Davis acknowledged that challenge in an interview Tuesday. “We don’t want to have a yo-yo effect,” he said. But “our learners can make another year’s worth of gains next year.”

The grades can also obscure widespread deficiencies in students’ skills. Published test scores show that in seven of the 14 schools that are being celebrated, more than half of all students scored in the lowest of five skill levels in math, reading or both.

Despite those limitations, Davis said, “gains are celebrated. That means we have students who are comprehending content. They have greater fluency and understanding of curriculum.”

He said the improvement is an indication that strategies introduced by his team are beginning to bear fruit. Schools last year used small group instruction and extensive student data to personalize instruction. While some teachers criticize diagnostic systems such as i-Ready and Achieve 3000, Davis said their use “allows us to identify a student’s strengths and areas of opportunity.”

He also credited leaders in the struggling schools for encouraging students who began the year in remote learning to return to school buildings, where educators agree they can get the best results.

The Transformation group, headed by longtime Hillsborough educator Shaylia McRae, is Davis’s version of initiatives that went by the names Priority, Elevate and Achievement under the last administration. All these initiatives tap state and federal resources to strengthen schools in impoverished neighborhoods, and aim to make the system more equitable.

Davis noted that, districtwide, Hillsborough’s improvements this year were better than in Miami-Dade, Broward and Palm Beach, the state’s other large districts.

“I think you celebrate everything you can,” Davis said. “You get to recognize the hard work of our students, our parents, our teachers, our leaders and our support staff while we recognize that we have work to do related to proficiency in literacy and mathematics.”

Looking ahead, he said, he wants students “owning their short-term and long-term goals, owning their data, owning the learning.”