The practices and perceptions of a shared planning team decision-making model and the effects on student achievement and attendance are examined in this study. Survey results, test scores, and background data on schools were utilized to analyze the relationships among the degree of shared decision-making and planning effectiveness ratings, student attendance, and mathematics and reading achievement to compare participant perceptions of the model and to determine the strength of predictor variables. A questionnaire was administered to a sample of 242 elementary and high school teachers, principals, and assistant principals in a larger urban school district (Chicago, Illinois), which yielded an approximate 75 percent response rate. Seventy-two percent of the respondents were teachers. Findings indicate that schools that ranked midrange on a shared decision-making index made greater gains in student mathematics and reading attendance than did higher or lower ranking schools. Shared decision-making was not found to be a significant predictor of student achievement and attendance; however, the percent of low income students was a powerful predictor. Higher ranking schools were more likely to have planning teams and more comprehensive curricula and to report improved communication and morale. Although current school-based management encourages increased shared decision-making, more participation may not be effective. Contingency theory is therefore useful in predicting the impact of planning models on student outcomes. An extensive bibliography, statistical tables, and a copy of the questionnaire are included. (LMI)