The purpose of this study was to compare the collaborating and communicating Turkish mathematics teachers with non-collaborating and communicating Turkish mathematics teachers in terms of their students' mathematics performance. A total of 4498 8th grade students and 146 school teachers from Turkey participated in the Trends in International Mathematics and Science Study (TIMSS) in 2007. The participants were those who completed all questions in the teachers' questionnaire teacher collaborations and students participated in the mathematics test. Independent t-test was used to identify differences if any among mathematics performance of students based on their teachers' involvement of lesson study. The results revealed that lesson study effects students' mathematics performance (c) 2011 Published by Elsevier Ltd.