Factor analytic procedures were used to gather validity evidence on the internal structure of Skinner, Kinderman, and Furrer's Engagement versus "Disaffection with Learning" measure to operationalize students' classroom engagement. Independent samples of middle school students (Sample 1 = 618, Sample 2 = 493) were used to test the scale's factor structure and invariance of measurement model parameters. Factor analytic results supported an alternative three-factor model of the scale's previously reported four-factor solution. Cross-validation was based on the use of multisample confirmatory factor analysis, which supported "strict factorial invariance" of the scale's measurement model parameters (e.g., factor loadings) across samples. Subscale reliability estimates, based on coefficient omega, exceeded 0.74. Implications of findings for research and practice are discussed.