Purpose: With no existing gold standard for comparison, challenges arise for establishing the validity of a new standardized Mandarin language assessment normed in mainland China. Method: A new assessment, Diagnostic Receptive and Expressive Assessment of Mandarin (DREAM), was normed with a stratified sample of 969 children ages 2;6 (years;months) to 7;11 in multiple urban and nonurban regions in northern and southern China. In this study of 230 children, the sensitivity and specificity of DREAM were examined against an a priori judgment of disorders. External validity was assessed using 2 indices of language production for different age groups. Results: External validity was assessed against spontaneous language indices (correlation range: r = 0.6-0.7; all ps < 0.01) and narrative indices (overall: r = 0.45, p < 0.01). Sensitivity (0.73) and specificity (0.82) of DREAM are moderate to good using a priori judgment as the standard. The values improved to 0.95 and 0.82 when spontaneous language and narratives were added to a priori judgment to define typicality. Divergent validity was moderate with nonlinguistic indices. Conclusion: DREAM holds promise as a diagnostic test of Mandarin language impairment for children aged 2;6 to 7;11.