The development of students’ critical thinking skills is an important part of a university education. The ArguEd project focuses on helping Computing and Technology (C&T) students improve their argument analysis and construction skills. At the heart of the project sits the use of a diagram-based technique for scaffolding argument analysis and construction. The technique, known as argument mapping, has been pioneered in Philosophy degrees. We investigate the specific challenges posed by using this technique in the context of distance learning for C&T students of a large (>2000 students) entry-level gateway module. Our approach includes innovative interactive computer-based formative assessment of argument mapping. We are evaluating the approach using data from formative and summative assessment, detailed analysis of student work, and feedback from both students and module tutors.