Figures revealed following a Freedom of Information request show that schools under the control of the local authority hired supply staff for the equivalent of 34,360 days since the 2013/14 academic year.
However, the use of supply staff is falling, with teachers used for a total of 12,737 days in 2013/14 – down to 10,434 days in the past academic year.
Today, union bosses said continued cuts to pay and conditions for teachers are among the main reasons for the need to frequently employ supply staff.