For administrators, teachers, students and their families in some districts, summer isn't what it used to be. Trying to stem a "summer slide" of learning loss by students and also to avoid having to build more schools to cope with overcrowding, districts are operating on year-round schedules that shorten the traditional summer vacation while adding breaks through the year, which traditionally averages 180 days of instruction, according to the U.S. Department of Education. But the results appear to be mixed, and some districts are backtracking on their strategies. President Barack Obama has called for longer school years to help American students compete with students around the globe, some of whom attend school up to 25 or 30 percent longer than American students.