The paper focuses on the influence of large-scale assessments on the concept of the Czech educational reform. At the beginning of nineties the Czech Republic joined IEA and later on became a member of OECD. The concepts of international comparative assessments and international debates about educational outcomes for 21st century influenced Czech policy makers and were the main impetus for the curricular reform that was launched in 2004. The designers of the reform, however, have not supported the reform by arguments based on national needs understandable to the Czech society. The reform was thus not accepted by the significant part of the Czech educational community and was implemented rather formally: the available data do not show any significant changes in teaching strategies or classroom educational objectives. Recently, the educational achievement of Czech students has been gradually (and significantly) declining. Academics, policy makers (including the minister of education) and most of teachers blame the reform. The professional community is not able to reach consensus on whether the decline was caused by the reform or by its uncompleted implementation. The paper also briefly discusses the findings of international large-scale assessments in the Czech Republic and their reflection in the Czech education policy.