Scientific argumentation is one of the core practices for teachers to implement in science classrooms. We developed a computer-based formative assessment to support students' construction and revision of scientific arguments. The assessment is built upon automated scoring of students' arguments and provides feedback to students and teachers. Preliminary validity evidence was collected in this study to support the use of automated scoring in this formative assessment. The results showed satisfactory psychometric properties related to this formative assessment. The automated scores showed satisfactory agreement with human scores, but small discrepancies still existed. Automated scores and feedback encouraged students to revise their answers. Students' scientific argumentation skills improved during the revision process. These findings provided preliminary evident to support the use of automated scoring in the formative assessment to diagnose and enhance students' argumentation skills in the context of climate change in secondary school science classrooms.