An organization is a context where its members are assigned tasks and learn from their work experiences. Although researchers agree that organization structure influences organizational learning, the literature has not forcefully examined its micro-level process. As an initiative effort, we tap the potential of the garbage can model and extend it to accommodate individual learning and knowledge diversity. While confirming the conventional wisdom regarding the specialization-coordination tradeoff, our simulation analysis reveals an underexplored merit of hierarchical structures: tightly constrained participation for low-level members promotes their specialization which helps, rather than hiders, dynamic coordination driven by high-level members under loose participation constraint and thus with broad experiences and knowledge. This advantage becomes pronounced when the organization faces more difficult problems and its members learn faster.