The paper examines how teachers' attitudes towards tracking (separating pupils into groups with different curricula on the basis of their abilities and results) differ among various generations of teachers. Fundamental and quick changes in the educational system occurred in the Czech Republic after the Velvet Revolution in 1989 as a unified educational system moved to a system strongly accenting tracking practices. We use this "policy discontinuity" to validate teacher socialization theory and test three alternative socialization hypotheses based on different key periods in teachers' development: the pupil experience hypothesis, the pedagogical preparation hypothesis and the pedagogical experience hypothesis. We work with a data-set from 2009 covering 1002 Czech teachers. The mean tests and the logistic regression analysis support the socialization theory, however only the pedagogical experience hypothesis was found to be most influential.