Study Time and Scholarly Achievement in PISA

We take a different look at the PISA 2006 data set considering time input as the main ingredient for scholarly achievement. Across countries, absolute time spent studying is negatively related to scholarly achievement, while a larger fraction of total study time spent in the classroom is associated to better performance. However, at the country level more total study time (class time plus homework time) is associated to better performance. When considering different groups of students, this positive relationship between time input and scholarly achievement breaks down. In particular girls and students with a migratory background spend more time in class rooms and doing homework but perform worse. We estimate a non-linear production function for education which allows us to consider marginal rates of substitution among various input factors for the production of education: different time inputs, family characteristics, and aspects of school environment. We find that compensating for less class time or lower socio-economic background by individual study time, is enormously time-costly or even impossible for students in Spain, as well as for students in the three best and the three worst performing OECD countries. Our results also show that in particular additional hours of class time rather than more teachers or better-equipped schools can compensate for a less advantageous family background.