The number of elementary and middle school students running out the school doors this month only to come back for summer school in July is set to more than double this year.

The city has identified 21,000 students in grades three through eight who, based on their low state test scores, will be required to attend summer school this year. That’s a major increase over the 10,000 students sent to summer school last year because of their test scores.

The explanation for that jump lies with a change in how the city and state are calculating which students passed the annual math and English exams. As a result of a delayed state testing schedule, the city is setting what it calls “promotional cut scores” meaning they will only be used to decide who is required to go to summer school. This year those cutoff scores are higher than in years past, causing more students to fall into the low-scoring range that compels them to attend summer school.

Schools still have some time to appeal the city’s decisions, meaning that the final number of summer school students could change.

The vast majority of summer school students are in high school, so the increase in elementary and middle school students is not likely to have a large impact on the school system as a whole. In 2009, out of over 100,000 summer school students, 90,000 were in high school.