Created by Tim Loane, the series follows a group of secondary school teachers in their daily lives. While the first series centres heavily around probationary teacher Simon Casey (Andrew Lincoln), later series have an ensemble approach. The cast changes dramatically over time, with few original characters remaining by the fourth series. While some of these disappearances are explained, others happen between series without explanation. The first three series are set in the fictional Summerdown Comprehensive, which merges with another school in the fourth series to form Wattkins School.