Assessing Teacher–Student Interactions in Physical Education for Sustainable Development: Validation of the CLASS-S Tool in the Polish Educational Context

Ensuring healthy living and promoting well-being (Sustainable Development Goals 3) is a key goal of school Physical Education. As many students in Poland perceive these lessons as unengaging and ineffective, there is a need to explore new educational strategies. One such approach is teaching through interaction, which emphasises the quality of teacher–student relationships. This study aimed to adapt and validate the Classroom Assessment Scoring System—Secondary for use in Polish Physical Education settings, considering the cultural context of Polish schools and the challenges of applying interaction-based frameworks in a traditionally structured education system. Fifty teachers from 24 schools recorded two lessons each, resulting in 100 video recordings. Lessons were analyzed using a structured observational protocol. Teacher–student interactions were recorded and coded by two trained observers. Confirmatory factor analysis confirmed excellent model fit (χ 2 /df = 1.158; CFI = 0.996; TLI = 0.998), and internal consistency was supported by Cronbach’s alpha. Inter-rater reliability was high, with intraclass correlation coefficients ranging from 0.928 to 0.946. The modified tool is both valid and reliable. Its application can enhance the evaluation and professional development of Physical Education teachers and support the integration of health- and education-related goals in school practice and contribute to achieving SDGs 3 and 4.