The relationship between vertical and shared leadership is gaining attention in leadership research. Past studies largely focus on their direct causal relationship and suggest that vertical leadership can promote shared leadership. This study moves further and attempts to explore how vertical leadership can enhance shared leadership in an information system development (ISD) project team through an interaction effect concept. Specifically, we first propose that value diversity reduces system quality through inhibiting effective shared leadership among team members. We further suggest that intervention from team leader can ease the negative impact of value diversity on shared leadership and remedy shared leadership on teamwork outcome.