No country or economy participating in PISA 2012 can claim that all of its 15-year-old students have achieved basic proficiency skills in mathematics, reading and science. Some 28% of students score below the baseline level of proficiency in at least one of those subjects, on average across OECD countries. Poor performance at age 15 is not the result of any single risk factor, but rather of a combination and accumulation of various barriers and disadvantages that affect students throughout their lives. Students attending schools where teachers are more supportive, have better morale and have higher expectations for students are less likely to be low performers in mathematics, even after accounting for the socio-economic status of students and schools.