Purpose: The Access to Literacy Assessment System--Phonological Awareness (ATLAS-PA) was developed for use with children with speech and/or language impairment. The subtests (rhyming, blending, segmenting) are appropriate for children who are 3 to 7 years of age. ATLAS-PA is comprised entirely of receptive items, incorporates individualized levels of instruction, and is adaptive in nature. Method: To establish construct validity of ATLAS-PA, we collected data from children with typical development (n = 938) as well as those who have speech and/or language impairment (n = 227). Results: Rasch analyses indicated that items fit well together and formed a unidimensional construct of phonological awareness. Differential item functioning was minimal between the two groups of children and scores on ATLAS-PA were moderately to strongly related to other measures of phonological awareness. Information about item functioning was used to create an adaptive version of ATLAS-PA. Conclusions: Findings suggest that ATLAS-PA is a valid measure of phonological awareness that can be used with children with typical development and with speech and/or language impairment. Its adaptive format minimizes testing time and provides opportunities for monitoring progress in preschool and early elementary classrooms. [This article was published in "Language, Speech, and Hearing Services in Schools" (EJ1270209).]