It is assumed that students’ academic achievement can improve if teachers’ academic optimism increases. However, this relationship seems to be mediated by individual citizenship behavior. With the aim of helping with the improvement of students’ academic achievement, in this research the mediation role of individual citizenship behavior is explored. To this end, a sample of 113 female teachers was randomly selected from among all teachers in the city of Karaj. The sample’s individual citizenship behavior and academic optimism were measured using two questionnaires. The students’ academic achievement was estimated by their mean scores on math and science courses. The validity and reliability of all instruments were confirmed. Data analysis using Pearson correlation and path analysis lead to a structural equation wherein the direct and indirect effects of teachers’ optimism on academic achievement can be detected. Results show that not only academic optimism directly and significantly affects achievement it also impacts it indirectly through individual citizenship behavior.