The appropriate selection of standardized tests is integral to establishing an accurate early diagnosis and providing timely treatment to optimize language outcomes in young children. However, clinicians sometimes utilize tests that are not validated for this specific purpose. This applied dissertation was designed to investigate the validity of the Communication Domain subtest of the Developmental Assessment of Young Children--Second Edition (DAYC-2) as a measure to diagnose a language disorder in preschool-age children when compared to a specifically designed language test in a large school district in Georgia. Diagnostic validity was considered via concurrent validity with the Preschool Language Scale--Fifth Edition (PLS-5). Data were collected from 105 preschool-age children in a large school district in Georgia. Multiple statistical analyses were used to determine the presence and nature of the connection between the two identified measures. Additionally, differences based on severity range, gender, and age were explored. The initial analysis revealed a statistically significant positive relationship between all subdomains of each measure. Furthermore, a correlational analysis yielded a strong, positive correlation between all subdomains of the tests. The subjects performed similarly across severity ranges on both measures. Gender was a significant covariant for receptive language, whereas age was a significant covariate across all subdomains. These results indicate that the Communication Domain subtest of the DAYC-2 and the PLS-5 are strongly correlated, thereby establishing concurrent validity between the measures and promoting the diagnostic use of the Communication Domain subtest of the DAYC-2 in preschool-age children. The Communication Domain subtest of the DAYC-2 may be useful in situations in which the PLS-5 cannot be administered, including readministration limitations, time and budget constraints, and lack of direct assessment ability. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]