The buses are running and kids have returned to school. Many call this the end of summer, especially given the cooler than normal weather that persisted for much of August. Others push the end of summer to the Labor Day holiday, which falls on September 4th this year. From an astronomical standpoint, summer ends and fall begins with the autumnal equinox, September 22, when day and night are roughly the same length. From a practical point, we tend to divide the months into 4 seasons, each 3 months long, with summer being June through August and Fall covering September through November.
Mary Knapp, Weather Data Library