Construct confusion and measurement challenges have plagued emergent literacy research for decades. Using a 2 × 2 × 2 factorial design, this study evaluated the dimensionality of alphabet knowledge and identified the sequence of development of 8 alphabet knowledge skills. Eleven models were evaluated in a sample of 3,692 preschool- and elementary school-age children. Findings supported a unidimensional conceptualization of alphabet knowledge that includes letter name knowledge and letter sound knowledge but not the ability to discriminate letters from nonalphabetic characters. Test information curves and significance tests of model constraints revealed reliable main and interaction effects of test format, capitalization, and component skills on items' discriminations and difficulties. Implications for improving the measurement of alphabet knowledge are discussed in recognition that doing so will support advancement of theory, research, educational practice, and ultimately student achievement.