s described in the preceding chapters, quality instructional design is partly science, partly art, but always a reflective, systematic application of research-based principles of teaching and learning. Most educators and training professionals, however, know the field only through its productsinstructional programs, units, mediated units, courses, and interventions that help learners (the consumers of instruction) achieve desired educational goals. But the development of successful products requires more than simply diligent effort, professional experience, and good faith by designers. As is (or should be) true for all fields that deliver products to consumers (automotive, medical, nutrition, sports, and others), evaluation is an essential component of the instructional design process: (a) as the products are being developed, (b) when they are in completed form and ready for release, and (c) as they are being employed over time. described the lack of evaluation in the development of educational materials in the late 1950s to mid-1960s as the go-go years marked by instructional materials in which instructional effectiveness was not a major factor. Komoski proposed the use of learner verification for instructional materials directed at K-12 education. Obviously, in the absence of evaluation, the instructional materials made available to trainers, teachers, and learners would be unrefined and untested based on valid and reliable empirical data, a potential disappointment and loss to the consumer and a black mark against the designer.