Studying development processes, as they unfold over time, involves collecting repeated measures from individuals and modeling the changes over time. One methodological challenge in this type of longitudinal data is separating retest effects, due to the repeated assessments, from developmental processes such as maturation or age. In this article,…

The purpose of this article is to describe preliminary psychometric characteristics of a student self-report measure of self-determination, the "Self-Determination Inventory: Student Report" version (SDI-SR), designed for youth with and without disabilities. We administered the draft assessment to 311 youth and examined item functioning…