Poland is one of the few European countries that achieved strong improvement of student performance over the last decade. According to the OECD PISA results Poland moved from below to above the OECD average and now is close to top-performing countries. The score improvements are a consequence of Polish education system reform introduced in 1999. The most important change of the 1999 reform was an extension of comprehensive education by one year. The evidence suggests the change immediately benefited student, while the remaining elements of the reform are probably responsible for the gradual improvement. The differences between secondary schools were largely limited. Introduction of nation-wide comparable exams, conducted at the end of every stage of education, played a crucial role in assuring quality in education system. Poland also increased support for the preschool education and further expanded the general curriculum in vocational schools. The result of all reforms was the expansion of obligatory comprehensive education from 8 years to at least 10 years now.