This is an empirical study of intonation errors made by a group of Spanish learners of English in secondary education. Errors relate to the division of the speech chain into tone units and to onset and nucleus placement within the tone unit, and are classed into interference errors (i.e. those mediated by the learners’ native language) and developmental errors (the rest). The study explains interference errors by reference to contrastive aspects of Spanish and English tonality (the division of speech into tone units), tonicity (intonation signalling of information focus) and onset placement. It refers to a strong relationship between rhythmic stress errors and intonation errors. The paper also refers to some institutional reasons behind the students’ low performance, and suggests some pedagogical remedies to deal with the errors detected.