Far too many students around the world are trapped in a vicious cycle of poor performance and demotivation that leads only to more bad marks and further disengagement from school. Students who perform poorly at age 15 face a high risk of dropping out of school altogether. By the time they become young adults, poor proficiency in numeracy and literacy can translate into limited access to better-paying and more rewarding jobs, poorer health and less social and political participation. When a large share of the population lacks basic skills, a country's long-term economic growth and equity are severely compromised. The newly released PISA report, "Low-performing Students: Why They Fall Behind and How to Help Them Succeed," looks at the factors that are most strongly associated with poor student performance. This issue of "PISA in Focus" highlights the following research findings on low-performing students: (1) 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 Organisation for Economic Cooperation and Development (OECD) countries; (2) 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; and (3) 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. [For "Low-Performing Students: Why They Fall Behind and How to Help Them Succeed. PISA," see ED565217.]