In the study described in this article a questionnaire was employed that can be used to assess students' and teachers' perceptions of science teachers' interpersonal communication behaviors in their classroom learning environments. The Teacher Communication Behavior Questionnaire (TCBQ) has five scales: Challenging, Encouragement and Praise, Non-Verbal Support, Understanding and Friendly, and Controlling. The TCBQ was used with a large sample of secondary science students in Taiwan, which provided additional validation data for the TCBQ for use in Taiwan and cross-validation data for its use in English-speaking countries. Girls perceived their teachers as more understanding and friendly than did boys, and teachers in biological science classrooms exhibited more favorable behavior toward their students than did those in physical science classrooms. Differences were also noted between the perceptions of the students and their teachers. Positive relationships were found between students' perceptions of their teachers' communication behaviors and their attitudes toward science. Students' cognitive achievement scores were higher when students perceived their teacher as using more challenging questions, as giving more nonverbal support, and as being more understanding and friendly. The development of both teacher and student versions of the TCBQ enhances the possibility of the use of the instrument by teachers.