The so-called zero period, which begins at 7:20 a.m., was introduced after Gunn's starting time was pushed back in 2011. This year about 300 Gunn students, or 15 percent of the student body, are enrolled in 10 different zero-period academic classes, which include some of the school's most demanding courses: AB Calculus, AP Stats, Algebra 2/Trig, Intro to Analysis Calculus and AP Economics. PE classes are also offered.