This article is the first attempt to validate the Entrepreneurial Intention Questionnaire (EIQ) in secondary education students. It is based on the Theory of Planned Behavior (TPB) and includes its constructs: attitude towards entrepreneurship, subjective norm, entrepreneurial self-efficacy, and entrepreneurial intention. The promotion of entrepreneurship in early education requires valid and reliable measures to assess the desired outcomes and evaluate the effectiveness of the interventions. The EIQ presents good psychometric qualities in a Spanish sample of high school students (N = 226): (a) The four-factor structure fits the data with factor loadings ranging between 0.378 and 0.862; (b) Each dimension presents satisfactory reliability results (above 0.7); and (c) The dimensions reproduce expected relationships with entrepreneurial attitudes. Additionally, competing models of the TPB have been tested to provide evidence to support a modified version of the original TPB model. Consequently, the EIQ is adequate for secondary education in Spain, being especially useful for longitudinal studies.