The calendar may say summer, but school is back in session -- or soon will be.

Fresno Unified and Madera Unified students resume classes today. Visalia Unified will begin Thursday and Clovis Unified will begin school in a week.

One of the first districts to welcome students back was Central Unified School District in Fresno. The district's 14,500 students returned to classrooms Aug. 11.

Nearly all Valley school districts are asking parents to be on the lookout for pertussis, more commonly referred to as whooping cough. Symptoms include severe coughing spasms that can last for weeks. School and health officials are requesting that parents make sure their child's immunizations are current.

California has reported 2,174 cases through July 27, a sixfold increase from the 349 cases reported through the same period last year. Seven infants have died of the disease this year.

Other things to look out for in some school districts are increased class sizes -- both Fresno and Central unified school districts will have more students in elementary classes after budget cuts eliminated some teaching positions.

Fresno Unified

Some Fresno Unified students will arrive on campuses in new buses powered by compressed natural gas. Thirty buses were paid for with a $5 million grant from the California Air Resources Board and the San Joaquin Valley Air Pollution Control District. The buses are less polluting and will reduce fuel costs.

At Duncan Polytechnical High School in central Fresno, a pilot preschool program launches today to better prepare neighborhood children for kindergarten.

Meal time will see a few changes, too. New breakfast and lunch items include yogurt with peaches and granola, and oven-baked curly fries, part of the district's effort to increase meal options and offer more healthy items.

Teachers and administrators will be using a new computer program called ATLAS, which stands for Achievement, Technology, Learning and Assessment System.

The program was developed by the district and Microsoft, and will be phased in to replace the PowerSchool and mainframe systems for tracking enrollment, scheduling, attendance and grades for the district's 73,000 students. Parents will be able to access the new system.

Other changes will be more visible: 13 elementary schools will be undergoing modernization, as will Tioga Middle School and Bullard High School. The upgrades are funded by Measure K bond money.

And there will be some new faces in charge at 19 schools. The principals were either promoted, transferred or hired at the schools.

-- Tracy Correa

Central Unified

The growing Central Unified School District, with schools located mostly west of Highway 99, has launched a new effort that uses student data to improve classroom instruction -- and, ultimately, student performance in class and on state assessment tests.

Superintendent Michael Berg said that although the district has used data in the past, this new effort is designed to spot trends that help explain why a class or group of students is struggling with specific subjects or skills.

Students might not notice the new instructional effort, but they will likely notice the renovations at Roosevelt, Teague and McKinley elementary schools. Central High School West Campus also was renovated.

And the district's alternative education school -- Pathway Community Day School -- has a new home. It is now at Nielsen and Teilman avenues in a building that is being leased from the Fresno County Office of Education.