Introduction. The Index of Learning Styles (ILS) is a questionnaire created to assess students’ preferences regarding how they learn. It was originally designed in English for university students. The objective of the present work is to adapt the ILS questionnaire to Spanish and validate this adapted version, taking into account the cultural characteristics and cognitive level of the recipients, namely Spanish students aged 11–15. Method. We used the Delphi method involving expert opinions for content validation and the Brown and Maydeu-Olivares model, an approach from the Item Response Theory, for construct validation (this model is recommended for forced-choice items). Results. We located new items in the data scrubbing process, which in previous research were missed using classical factor analysis. The results for the global fit of the model show that 32 of the 44 items in the original questionnaire, display optimal values in various indices (RMSEA, CFI, X2, among others), and so this instrument can be used to identify learning style preferences in Spanish adolescents. Discussion. The Brown and Maydeu-Olivares model takes into account the nature of forced-choice items and this is the first the first time it has been applied to the ILS questionnaire. This validation procedure is novel and proves to be an optimal validation method for questionnaires with this type of items. The interest in the ILS questionnaire is due to the dimensions it assesses, which provide teachers and students with information about learning preferences for better psycho-pedagogical orientation and for the design of more personalized educational interventions.