The first is the “single-track” modified calendar, also known as a “balanced calendar.” The second is the “multi-track calendar.” Neither one is typically an extended year. Instead, both calendars involve moving the 180 school days around so that there are multiple short breaks as opposed to the typical long summer break.

Single-track calendars have all students following the same schedule. This balanced calendar often includes intersessions that provide additional opportunities for learning rather than “summer school.” With a multiple-track calendar, usually created to alleviate school overcrowding, some students are on campus while others are on break.

Balanced calendars often take the form of 45 school days followed by 15 days of break, or 60 school days followed by 20 days of break. Other kinds of modified calendars with shorter intersessions exist in states like Mississippi and South Carolina.