It is assumed that open and distance learning institutions develop study materials that can adequately engage learners with quality content that ought to contribute to their content mastery. However, despite interventions distance learners continue to underperform compared to those in the traditional classroom system prompting the concern that high drop-out and failure rates may be ascribed to the study materials. This mixed-methods case study - undertaken in Botswana - investigated the design and development of instructional study material as possible barrier to content accessibility. The study was informed by Sweller s Cognitive Load Theory (1980) which was used to evaluate the process of designing and developing instructional materials while Gorsky, Caspi and Trumper s Theory of Instructional Dialogue (2004) facilitated assessment of interaction with and within the selected study materials. The participants - five material developers, 176 learners and six tutors - were purposively identified and representative of remote, rural and urban sites. A document analysis of study materials was carried out as well as six semi-structured group interviews and twenty individual face-to-face interviews. A questionnaire survey was also undertaken with all the participants. Manual coding and SPSS were used for data analysis. Major findings of the study were clustered into three themes: inefficiency, inadequacy and imprecision with a key finding linked to English being used as a language of instruction. Non-alignment of materials with learner profile, language proficiency and the national syllabus remain problematic. The ODL institution concerned ought to establish a policy for quality assuring effective content design and development while the inclusion of information and communication technologies may create a more interactive learning experience, thus improving content mastery and academic progression.