Since facilitating the fullest development of each student in terms of enriching their intellectual development as well as their personal, social, and emotional development has become an important objective, social and emotional guidance has become an integral part of education. This recent acknowledgment has stimulated research interest into how to measure, evaluate, and optimize guidance activities in schools. This interest, however, is contingent on a valid assessment of integrated socioemotional guidance, which despite the growing attention still remains a problem. This study therefore aims to investigate the validity and generalizability of the Socio-Emotional Guidance Questionnaire (SEG-Q). Measurement invariance across three groups of teachers teaching in different stages of secondary education (Total n = 3,336) was tested, by means of multigroup confirmatory factor analyses (MGCFA) in Mplus. The results show partial invariance of the SEG-Q across the teacher groups, confirming that the SEG-Q is a psychometrically sound self-report instrument for secondary education teachers which can be used by researchers and practitioners to measure, map, describe, or evaluate integrated socioemotional guidance.