The present study aims to investigate language learners’ cognitive processes in on-line ESP courses. Three modes of inquiry are used: think-aloud protocol analysis, screen capture analysis, and correlation analysis. The theoretical foundations for the evaluation of the cognitive aspect of Ferdowsi Univeristy of Mashhad E-learning System are drawn from cognitive load theory, cognitive apprenticeship theory and human-computer interactivity theory. 15 users were interviewed while their performance on the screen was recorded electronically. The results of qualitative and quantitative analyses show that design features have a meaningful effect on the users’ performance in four phases of cognitive interaction with e-learning systems. The educational implications of the findings for software developers are discussed.