Despite considerable interest in research and practice in the effect of classroom disciplinary climate of schools on academic achievement, little is known about the generalizability of this effect over countries. Using hierarchical linear analyses, the present study reveals that a better classroom disciplinary climate in a school is significantly associated with better school reading performance in 53 of the 65 Programme for International Student Assessment (PISA) 2009 participant countries. The classroom disciplinary climate of schools can explain 11% of the between-school differences in reading achievement over countries. Controlling for economic, social, and cultural variables and student gender-related variables at student and school levels, the between-country differences in the effect of classroom disciplinary climate of schools shrank by three quarters. These findings can inform countries that face educational inequality issues (e.g., Argentina) and gender gap issues (e.g., Trinidad and Tobago), suggesting the possibility of tackling these issues via intervening on classroom disciplinary climate of schools.