A study evaluated the psychometric properties of the five-item Session Evaluation Scale (SES-P) for patients and the therapist-rated version (SES-T). Two independent samples, comprising 1,043 adult psychotherapy patients and 151 therapists, participated in the assessment. Researchers conducted various analyses including item response theory and confirmatory factor analysis to evaluate reliability and validity. Results showed that both the five-item patient and therapist forms had strong psychometric properties, with excellent internal reliability and a clear unidimensional structure. The five-item versions also demonstrated full measurement invariance across in-person and video sessions for patients. Additionally, three-item versions of the scales maintained good psychometric properties and showed strong agreement with the five-item scores, indicating minimal bias. Overall, the SES-P and SES-T, particularly in their shorter forms, are reliable tools for assessing session quality in psychotherapy.