Finnish teacher educators with the research background joined in a common enterprise to gather information from the Finnish education system and used practices in teaching science and mathematics to explain the Finnish students’ success in the international PISA (Program for International Student Assessment) assessment. The items dealt with were the following: the Finnish school system and teacher education, learning environments, gender issues, influential factors outside the school, and teaching science and mathematics at the comprehensive school. From the articles by 40 authors the book “How Finns Learn Mathematics and Science?” was produced. The explanations for Finnish success based on the authors’ conceptions can be classified into three groups: Teacher and teacher education, school and curriculum, and the national developmental projects. Most probably a true explanation will be a combination of several factors as no single clear explanation was found, although research-based teacher education seems to be a rather influencing factor.