From the perspective of parallel mixed-methods research, this paper describes interactivity research that employed usability-testing technology to analyse cognitive learning processes; personal learning styles and times; and errors-and-recovery of learners using an interactive e-learning tutorial called "Relations." "Relations" presents mathematical content for Theoretical Computer Science 1. It incorporates instructional content, scaffolding to support learning, worked examples and exercises. The findings from combining quantitative and qualitative studies were synergistic as they confirmed each other and also complemented each other when one data collection strategy provided insights and details not obtainable from the other. Data was mapped against concepts from the literature. This work makes methodological and practical contributions.