This paper addresses a new approach to prepositions in primary and secondary education, particularly in upper secondary school. For that purpose it is recommended that the heterogeneity of the language system, linguistic variation and Sociolinguistic Theory should be discussed in the classroom. Then, the paper presents a variationist study of the possibility of alternating prepositions. The paper proceeds with the proposal of constructing an approach to this grammatical component for upper secondary school pupils. The conclusion resumes the importance both of linguistic research to the teaching of Portuguese and of an appropriate teaching methodology to avoid prejudice in relation to language varieties not acquired at school.