The aim of this study is to explore the concurrent validity of the Behavioral Inhibition Scale 3-6 (BIS 3-6), a scale created for the early detection of the temperamental disposition toward social anxiety. Seventy-three participants were randomly selected from a wide sample of preschool-age children to undergo systematic observation using the Behavioral Inhibition Paradigm. Parents and teachers rated the BIS 3-6. Clinicians and researchers also measured behavioral inhibition. The BIS 3-6 scores correlate between r = 0.2 and r = 0.6 with the observational indicators, and all correlations are in the expected direction. A discriminant analysis supports a good capability of the BIS 3-6 scores to identify extreme inhibition. Consistent with previous research and given the discrepancy among parent and teacher reports and observational measures, the moderate convergence among the BIS 3-6 trait-measurements and the observational state-measurements support the validity of the BIS 3-6 scores. This study advances the validation process for a new tool intended to early detect impairing behavioral inhibition.