This article focuses on the effectiveness of computer-based instruction (CBI) screen designs, including their benefits and limitations, as well as human constraints in designing effective CBI. The paper begins with an overview of what comprises an effective CBI screen design, including characteristics of human factors, how information must be visually presented to stimulate and enhance human comprehension, how physical actions must flow to minimize the potential for fatigue and injury, and consideration of the capabilities and limitations of the hardware and software at the human computer interface. Benefits of a well-designed CBI screen are summarized, including effects on general academic performance and cognitive outcomes, as well as the advantages of graphic presentation of information. The following problems that may impact the usability and effectiveness of a CBI medium are discussed: constraints in design guidelines; human constraints; hardware constraints; application considerations; and design complexity and inconsistent terminology/techniques. It is concluded that different CBI screen design interfaces have different strengths and weaknesses. Some concepts and tasks are very difficult to convey symbolically and are not suited for a CBI screen design; other concepts and tasks may be well suited. Which tasks are best suited for which styles and systems still needs much study. (Contains 29 references.) (AEF)