The Early Learner Curriculum and Achievement Record (ELCAR, Greer et al., 2020) is a criterion-referenced curriculum and assessment of children's development of language and social repertoires from the earliest foundational observing responses to advanced verbal repertoires. The developmental cusps or stages identified in the ELCAR have been validated and replicated through rigorous single-subject studies, but the assessment's convergent and divergent validity with traditional psychometric measures of similar and dissimilar constructs have not been investigated. In the present study, we compared one component of the ELCAR, the Verbal Behavior Development Assessment--Revised (VBDA-R), to four traditional psychometric measures as well as observed joint attention between 42 mother-child dyads within a free play setting. The preschoolers attended a full day applied behavior analysis (ABA) school that served children with autism spectrum and related disorders. The VBDA-R demonstrated convergent validity with the Vineland Adaptive Behavior Scale--3 (Vineland-3) Teacher Rating Form Communication domain, Autism Diagnostic Observation Schedule--2 (ADOS-2) module, and observed child-initiated joint attention (IJA). It demonstrated divergent validity with the Sensory Experience Questionnaire (SEQ), Child Behavior Checklist externalizing scale (CBCL/1.5-5), and child response to mother-initiated joint attention (RJA).