This paper looks at underlying patterns of school effectiveness through analysing a GCSE examination data-set over a period of ten cohorts (1993-2002) in one very large English school district. Both value added and raw score approaches were explored by employing different statistical multilevel models to examine time trends of school and pupil performance from two perspectives: consistent (linear) and inconsistent (non-linear) school improvement. Overall, levels of measured attainment for the vast majority of the schools increased over the decade and the results indicate that one in four schools had significantly higher value added improvement trajectories (linear) than would be expected over the decade--in comparison to the average school. Those schools with a lower value added starting point in 1993 were more likely to make significant improvement. However, underlying these linear improvement trajectories it appears that only one in 16 schools managed to improve "continuously" for more than four years at some point over the decade in terms of value added. (Contains 2 figures, 6 tables and 4 notes.)