The world over, secondary school science is viewed mainly as a practical subject. This may be one reason why effectiveness of teaching approaches in science education has often been judged on the kinds of practical activity with which teachers and students engage. In addition to practical work, language--often written (as in science texts) or oral (as in the form of teacher and student talk)--is unavoidable in effective teaching and learning of science. Generally however, the role of (instructional) language in quality of learning of school science has remained out of focus in science education research. This has been in spite of findings in empirical research on difficulties science students encounter with words of the instructional language used in science. The findings have suggested that use of (instructional) language in science texts and classrooms can be a major influence on the level of students' understandings and retention of science concepts. This article reports and discusses findings in an investigation of physics teachers' approaches to use of and their beliefs about classroom instructional language. Direct classroom observations of, interviews with, as well as content analyses of the participant teachers' verbatim classroom talk, were used as the methods of data collection. Evidence is presented of participant physics teachers' lack of explicit awareness of the difficulty, nature, and functional value of different categories of words in the instructional language. In conclusion, the implications of this lack of explicit awareness on the general education (initial and in-service) of school physics teachers are considered.