The increasing cultural diversity in the current Spanish educational system has had dramatic consequences for school population demography and relationships between students in culturally diverse classrooms. In this context, the development of students' intercultural competence can contribute to strengthening communication, as well as preventing misunderstandings and coexistence problems. In this study, the effects of a teacher-led intercultural tutoring action programme (TAP) on elementary students' intercultural competence (IC) were assessed as a function of treatment condition and grade level. Participants were 187 third- to sixth-grade pupils (84% Spaniards and 16% immigrants) who were assigned randomly to treatment conditions (TAP versus comparison). After 20 weeks of programme implementation, the findings revealed that the TAP was successful. Conceptual intercultural competence was better achieved by fifth- to sixth-grade students, while IC skills and attitudes were significantly better developed by third- to fourth-grade students. Implications for teachers and counsellors/schools psychologists are discussed.