In this article I study the sharp decline in performance experienced in 2015 by the Basque Country region (Spain) in secondary education student outcomes, as measured by the OECD’s PISA assessment. I construct a harmonized and comparable dataset for the Basque Country since 2003 and examine how differences in observable student and school characteristics have affected changes in student outcomes. Despite the economic crisis experienced by the Basque economy since 2008, the increase in socioeconomic characteristics of students slows down but does not decrease in 2015, hence having little effect on the decline in performance. Conversely, I find three factors that may help explain part of the decline in scores since 2009 and 2012 and which affect students across all the performance distribution: an increase of repeaters, an increase of students which take the test in a language different from their regular language at home, and the perceived increases by the school principals in student behavior problems at school. The results call for a cautious response and interpretation by public authorities given the low-stakes nature of the PISA test and the diversity of factors affecting the decline.