Purpose: The current study aimed to understand the clinical decision-making skills of school-based speech-language pathologists (SLPs) using narrative and expository discourse information from three sources: perception of language through listening to language alone, standardized criterion-referenced narrative assessment data, and word- and morpheme-level language sample analysis data. Method: Twenty-eight current school-based SLPs participated in the study. During this study, participants rated language quality and made decisions regarding the provision of language services after being provided information from informal assessment measures. Results: SLPs' ratings of language quality and complexity varied across the story retell, wordless picture book generation, and expository samples. There was a lack of consistency in ratings within each context across areas of clarity, sample complexity, language complexity, and vocabulary across all SLPs. Self-reported factors that influenced SLPs' ratings included components of structure, syntax, and semantics. SLPs did not indicate a need for services after listening alone. When provided with criterion-referenced narrative assessment scores and word- and morpheme-level language sample data, more SLPs made a recommendation for services. Conclusions: The study demonstrates the need for objective language measure data during diagnostic decision making. Additionally, SLPs may not realize the information obtained from real-time perception, and analysis of language samples may be an unreliable and inconsistent picture of a child's language abilities. The results of this study highlight the need to continue to rely on multiple sources of assessment data. SLPs should continue to incorporate systematic methods to minimize variability of perceptions in the process of making diagnostic decisions.