The authors demonstrate the increment of clinical validity in early childhood assessment of physical impairment (PI), developmental delay (DD), and autism (AUT) using multiple standardized developmental screening measures such as performance measures and parent and teacher rating scales. Hierarchical regression and sensitivity/specificity analyses were used to identify the differential impact of each domain the scales measure. Significant findings include (a) self-help domains in either parent or teacher questionnaires are more significant contributors than social-emotional domains to early detection, (b) performance measures are stronger predictors than parent or teacher questionnaires in detecting physical impairment or developmental delay, and (c) parent questionnaires measuring self-help skills are a stronger predictor of autism than performance measures. These results support the combined use of parent and teacher rating scales and provide important implications in choosing instruments for different developmental disorders when time and resources are limited.