Scientific literacy is an important goal for science education, especially within controversial socioscientific issues. In this study, we analysed 143 students' research reports about stem cell research (SCR) for how they addressed specific source evaluation criteria provided within the assignment. We investigated students' opinions about SCR, how they used the evaluation criteria to evaluate online sources and whether the evaluation criteria and/or the specific sources influenced their opinion and/or understanding of SCR. We found that most of the students supported some form of SCR and reported that their sources were credible and contained more factual information than opinions. Students critiqued the language of the authors, as well as status in their respective fields, along with the content within each source. Additionally, students reported that their sources influenced their content knowledge, but had little influence regarding their SCR opinions. Through this work, we present a new working model and suggest the need for additional research about the understudied interface of opinion, understanding and evaluation within the context of important socioscientific issues. Students' opinions and content knowledge, located at the model's centre, influence and are influenced by the research topic, the sources used, the evaluation criteria and the evaluation of the sources that students use to provide evidence for claims.