The purpose of this thesis was to identify a number of important factors or school inputs that affects pupil performance, measured by the PISA-score. Furthermore, the relative importance of the schooling inputs have been estimated and from the estimated model recommendations of how the Swedish schooling system might improve has been given. In order to estimate the econometric model a pooled OLS approach has been used. This implies that direct comparisons between individual countries was not possible to make, but which and how the variables affects the PISA-score have been identified. Based on the results two main recommendations of how Sweden may improve the schooling results has been given. The first is that the relative teacher wages needs to increase in order to enhance the relative status of teaching and attract high quality teachers’. The second is to increase the amount of time spent on physical activity in Swedish schools.