This study explored how human resource (HR) leaders' biased perceptions of frontline manager (FLM) effectiveness influence HR ratings of FLM competencies, resulting in insufficient training and job preparation for these critical employees. The literature review examined FLM research, ratings of supervisory competencies and the underlying theoretical frameworks of implicit leadership theory and leadership categorization theory, and their relationship to informal learning. The research used mixed methods, with a qualitative critical incident study to identify competencies, followed by a quantitative survey to compare ratings, followed by qualitative in-person interviews to confirm survey findings. Results revealed a significant difference between HR and other raters of FLMs, including the FLMs themselves, with regard to FLM effectiveness, and these differences are informed by HR stereotypes of FLMs. Recommendations and implications suggest HR's role in providing unbiased assessment could lead to essential FLM training and development.