As a result of the use of random assignment to treatment, randomized experiments typically have high internal validity. However, units are very rarely randomly selected from a well-defined population of interest into an experiment; this results in low external validity. Under nonrandom sampling, this means that the estimate of the sample average…

This ethnographic case study was designed to investigate a successful professional development model, perceived effective professional learning and process for determining professional development for teachers. With eighty years of research on professional development, limited research was available on the process for determining professional…