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 study demonstrated the effectiveness and efficiency of a constant time delay procedure (four seconds) to teach five elementary students with learning disabilities multiplication facts. Learning generalized to a paper-and-pencil task, to a different presentation orientation, and to reverse facts. (DB)

A multisensory program using a counting technique was effective in teaching math skills to three elementary students with mild disabilities. Results showed significant gains in acquisition of target skills as well as maintenance and generalization to novel math problems. (Author/DB)