This article presents some of the results obtained from our observation of three Secondary School Mathematics teachers pedagogical practice when they used mathematical language to teach "functions". From a qualitative data analysis some representative categories of conceptions raised in the classroom about the subject are proposed from the expressions effectively used by the teachers with their students. Some considerations are also raised on the relation between these conceptions and the use of a specific language to deal with "functions" in the teaching of Chemistry and Physics.
functions; teachers' conceptions; mathematical language; Mathematics, Physics and Chemistry teaching