The implementation of computer-based assessment (CBA) in PISA and the OECD's intention of relying only on this from 2015 suggests the need to evaluate to what extent it provides us with the same information as traditional paper and pencil assessment (PPA) conducted until 2012. Our results show that there is a significant gap between PPA and CBA for Spanish students that can be explained by factors such as availability and access to ICT or students' socioeconomic and cultural status. This leads us to conclude that educational policy reforms based on PISA scores and on any of these factors which affect them, as well as the comparison of these results along time, should be made in light of the specific assessment method used as reference.

Key words: computer-based assessment, paper and pencil assessment, gap.
Clasificación JEL: I20, I21.