In the development of distance learning, advances in cognitive science merge with new technology to deliver instruction worldwide. However, one major difficulty in evaluating the efficacy of these tools is determining which elements of instruction truly lead to observed changes in student performance. The purpose of this paper is to briefly review current use of various research methods for evaluating instructional technologies, discuss previous solutions to balancing the conflicting demands of internal and external validity, and then to propose a new research design that achieves this goal in a manner compatible with many instructional technology applications. The design, called a Strand of Pearls design, leverages the practice of delivering instruction in sequential modules to generate robust findings for which claims of internal validity, external validity, and maximal generalizability can be made.