Converging evidence shows that children's knowledge of letter forms, names, and corresponding sounds, collectively termed alphabet knowledge, are critically important emergent literacy skills that uniquely predict children's later reading success (Lonigan, Schatschneider, Westberg, & The National Early Literacy Panel, 2008; Schatschneider, Fletcher, Francis, Carlson, & Foorman, 2004). Due to differing experiences with and exposure to print, young children exhibit highly variable levels of alphabet knowledge (McBride-Chang, 1999; Piasta, 2014; Schatschneider et al., 2004). Early childhood educators therefore need to accurately measure and monitor children's alphabet knowledge to ensure they are making adequate progress in these foundational skills. The newly developed Letter-Sound Short Forms (LSSFs; Piasta, Phillips, Williams, Bowles, & Anthony, 2016) show promise as an ongoing assessment of children's alphabet knowledge. In the current study, we provide further evidence concerning the validity of this measure. Alphabet Assessment to Inform Instruction With increased awareness of the importance of alphabet knowledge for success in kindergarten and beyond, many early childhood educators administer some form of assessment to evaluate children's alphabet knowledge. To maximize the relevance of such assessments, educators need instruments that assist them in connecting children's scores to their instructional decision-making to facilitate explicit and systematic differentiated alphabet instruction (Phillips & Piasta, 2013; Piasta, 2014; Piasta & Wagner, 2010a). Such instruction requires ongoing progress monitoring of individual children's learning. Effective progress monitoring tools exhibit strong psychometrics, utilize multiple equivalent forms, show sensitivity to changes over time, and are brief and easy to administer and score (Kelley, Hosp, & Howell, 2008). Research has shown that educators who use the results of progress monitoring to inform their instruction have children who make greater gains (Ketterlin-Geller, Gifford, & Perry, 2015) and may be better able to identify children in need of supplemental instruction. Although many different alphabet knowledge assessments are available, existing tools are not ideal. Commercially available measures are typically valid and reliable but sometimes costly and may not be feasible for schools to purchase 737514A EIXXX10.