At GPS, as with its competitors, one of the most popular courses focuses on New York City’s Specialized High School Admissions Test, an entrance requirement for eight of the city’s nine specialized high schools. (LaGuardia High, a performing-arts school, has an audition system.) Less than 20 percent of eighth graders who take the exam clear the minimum score needed to get into a specialized school, including — at the most competitive end — Stuyvesant High School, Bronx High School of Science and Brooklyn Technical High School. A typical summer class for this test at GPS lasts three hours a day, every weekday, and can cost around $1,400. But Yan says virtually all his students get into a specialized high school. He knows this because he hands out Visa gift cards once results come out: $50 for Stuyvesant, $30 for Bronx Science, $20 for the others.