This mixed method research study is situated in the school effectiveness research paradigm to examine the correlation between the effectiveness of urban, primary school principals and their students' performance in mathematics. Nine, urban, primary schools from Negombo, a coastal fishing area in Sri Lanka, were selected; their student achievements in mathematics were documented in a longitudinal study from 1998 to 2002. At the end of 2002, principals in these schools were interviewed to obtain evidence of their effectiveness in six areas: (a) school vision, (b) decision-making process, (c) curriculum process, (d) staff development, (e) community relations, and (f) managing changes and challenges. The results indicate a measurable correlation between school performance and principal effectiveness. However, these results should be cautiously interpreted since there are other contextual factors that affect the functioning of these schools. The results also illustrate some challenges faced by principals in their day-to-day activities in coastal, primary schools in Sri Lanka.