Evaluating construct validity and internal consistency of early childhood individualized family service plans

•We conduct a psychometric evaluation of individualized family service plans (IFSPs).•Rasch measurement model is employed to investigate the scale's functioning and fit.•Highest rated items were those connected to basic skills or required by law.•Difficult items were indicative of higher skills, beyond simple mastery of lower skills.•Rasch analysis allows a new lens to examine and improve important measures.

This study presents evidence regarding the construct validity and internal consistency of the IFSP Rating Scale (McWilliam & Jung, 2001), which was designed to rate individualized family service plans (IFSPs) on 12 indicators of family centered practice. Here, the Rasch measurement model is employed to investigate the scale's functioning and fit for both person and item diagnostics of 120 IFSPs that were previously analyzed with a classical test theory approach. Analyses demonstrated scores on the IFSP Rating Scale fit the model well, though additional items could improve the scale's reliability. Implications for applying the Rasch model to improve special education research and practice are discussed.