Purpose A normative study using the Multiple Auditory Processing Assessment-2 (MAPA-2; Schow et al., 2018) was recently completed. With access to these data, the authors extend that work and support a definite construct for auditory processing disorder (APD). The goal here is to examine MAPA-2 reliability and validity (construct, content, and concurrent). Evidence for the APD construct is further buttressed by measures of sensitivity and specificity. Results of MAPA-2 testing on children diagnosed with learning disability (LD), attention-deficit/hyperactivity disorder (ADHD), and specific language impairment (SLI) are included. Method Normative data (previously published as the MAPA-2) allowing derivation of these findings included a representative sample of 748 children (53% girls) ages 7-14 years tested by 54 speech-language pathologists and audiologists in 27 U.S. states. The authors examined diagnostic accuracy based on the American Speech-Language-Hearing Association (2005) criteria (index test) for confirmed cases of APD. The index was also used to identify listening problems for three other diagnostic categories (LD, ADHD, and SLI). Validated questionnaire responses from parents and school personnel allowed incorporation of functional measures widely supported in APD diagnosis but unavailable with other normative and sensitivity/specificity studies. Results Reliability and validity were both satisfactory, and diagnostic accuracy for an APD group of 18 (28% female) compared to the remaining typical group of 625 yielded 89% sensitivity and 82% specificity. The remaining three groups (LD, ADHD, and SLI), where comorbidity was expected to be about 50%, had APD-type listening problems with a prevalence ranging from 52% to 65%. Conclusions Current results provide important evidence for the construct of APD. The MAPA-2 can be administered by an audiologist or speech-language pathologist. A similar diagnostic protocol in Australia yielded positive therapeutic gains. Further study is encouraged to determine if the present positive findings will be found in future research.