Purpose: This study aims to investigate how physical education teachers analyze their students' swimming skills. Particular attention is given to information gathering within the diagnostic process. Methods: Data were collected from a quantitative online survey of German physical education teachers from primary and secondary schools (n = 551). This survey's questionnaire is based on evaluated statements from a qualitative interview study (n = 10). Findings: Teachers' diagnostic approaches vary greatly and differ in terms of quality criteria and usability. The predominant method used is movement observation, but 50.3% of the teachers do it rather rarely or without the use of criteria. Many of them (63.8%) would like to be supported by a diagnostic tool for the analysis of swimming skills. Discussion/Conclusion: It has been concluded that an accurate analysis of the students' swimming skills as a precondition for adaptive lesson structuring is not achieved. It is necessary to determine whether a diagnostic tool could improve this process.