In the study, the effect of Predict-Observe-Explain (POE) activities carried out within the scope of argumentation-supported learning method on the detection of the conceptual understandings of the pre-service science teachers about "Solutions: Dissolving-Melting" was examined. Based on this main purpose, a case study was applied in the study, one of the qualitative research methods. The study group of the research consists of 22 pre-service science teachers. According to the data obtained at the end of the study, it was observed that pre-service teachers structured non-scientific claims and justifications, and could not use their refutation skills adequately before applications. It was observed that pre-service teachers were more willing and competent in developing scientific arguments in POE activities.