An important unanswered question concerns the question of intervention dosage i.e., the extent to which the amount of intervention that children receive affects the outcomes. In particular, there is a question about whether there is a threshold of minimum amount of an intervention that is required to produce desired child outcomes. One of the problems with research in this area is that currently, researchers do not have a common approach for how to define and measure dosage (e.g., number of lessons, length of lessons, number of days, extent of individual versus group instruction). Dosage is typically conceptualized as the overall amount of instruction offered. However, some researchers suggest that dosage should be conceptualized as a function not only of what is offered but also what is received by children. Further, measuring what is received by children may go beyond the child's exposure (i.e., time in a classroom) to their level of engagement with the intervention. Also, it is likely that the relationship of dosage to outcomes may be mediated by the quality of the intervention. The effect of dosage is likely to be different if the intervention being provided encompasses high-quality versus lower-quality practices. Future research will need to address the definitional issues surrounding dosage (offered or received) and the potentially complicated relationships among dosage, quality and features of the intervention being tested, and amount of dosage experienced by children.
The issue of dosage is a question in the area of professional development as well. Is there a dosage level of training to ensure sustained changes in teacher practices to ensure sustained changes in teacher behavior? Measuring dosage or intensity of professional development is not typically a part of evaluations. Even when descriptive data are provided, typically the data are about training sessions as opposed to the amount of coaching/mentoring, which is more difficult to measure. As a result, there is little evidence about the level of intensity of coaching that is beneficial and for whom. Future research should not only measure and report the intensity of interventions being studied, but also contrast varying intensities of instructional support provided to students to determine how much is necessary.
Further exploration of these dosage issues (e.g., definition, measurement, the intensity required to produce sustained outcomes) are necessary to further our understanding of how to ensure that all children are ready for and successful in school.
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