Elementary schools in many countries record an unequal representation of male and female teachers with female teachers in huge majority. At the same time, numerous studies reveal that girls generally outmatch boys in the majority of school subjects. Consequently, possible effects of teacher-pupil gender interaction are becoming an important topic in studies on pupils' school achievement. The aim of the present study was to examine the proposed teacher-pupil gender interaction effect on pupils' school achievement in Croatian elementary schools. The nationwide sample of pupils and their teachers from all 844 Croatian elementary schools was used. There were 48,232 pupils at the age 10 and 46,196 pupils at the age 14 in the research. Two types of pupils' school achievement measures were assessed--school marks and standardized knowledge tests for almost all subjects in school curriculum. Results indicate that girls generally outmatch boys by school marks, whereas results are equivocal when standardized tests were used. The teachers' gender effect measured by knowledge of their pupils reveal the superiority of female teachers, but only on standardized achievement tests. The interaction effects of teachers' and pupils' gender on school achievement are generally insignificant. The stability of these results was confirmed in both age cohorts and assumption that differences in boys' and girls' school achievement are related to teachers' gender cannot be supported within Croatian elementary education.