Teaching socioscientific argumentation (SSA) is a challenging task. One difficulty is the assessment of students’performances. Based on an earlier framework for teachers’ assessment of SSA (TAF), we developed a model called PracticalAssessment of Socioscientific argumentation Model (PASM). The aim of this study is to present PASM and explore how pre-service science teachers (PSTs) develop their skills in assessing SSA by using PASM. Ten science PSTs were asked to preparearguments for and against the use of nuclear power and GMO. PASM comprised several rounds where the PSTs (divided intosmall groups) argued in favour of, or against, the topic discussed, or acted as examiner assessing the argumentation. Afterthe PSTs had tried all roles, including regular discussions where the examiner gave feedback to those arguing, the SSI shiftedfrom nuclear power to GMO and the whole cycle was repeated. Data were collected as audio-recordings of the groupdiscussions, field notes taken by both authors during joint discussions and PSTs individual written reflections, and wereanalysed using thematic analysis. Six main themes and several subthemes were identified in the data analysis: focus in theassessment, the tools in PASM such as the matrix and TAF, the nature of PASM, such as the roles and iterative cycles, andcoping strategies. The exercise made PSTs aware of the quality criteria that should be included in assessment of SSA. Thenature of PASM, with its iterative cycles and repeated reflections, expanded PSTs view of SSA assessment, which showed aprogression through the different stages of data collection. We conclude that it is of great importance to include trainingassessment of SSA in teacher education and that using the PASM model could be one way of doing this.