Exposure to complex mathematics concepts and tasks is related to higher performance in PISA among all students, including socio-economically disadvantaged students. Working on complex problems without individualised support can increase mathematics anxiety among weaker students. In most PISA-participating countries and economies, at least one in two students attends schools where teachers believe that it is best to adapt academic standards to the students’ needs. Teaching strategies that support struggling students in mixed classes, such as giving students extra help when they need it, are related to students having more confidence in their mathematics ability.