A basic assumption about school enrollment is that classrooms are stable over the school year. Patterns of student mobility, teacher strategies for student orientation, teacher perceptions of mobile students, the effects of student mobility on principals' decision making, and the relationship between principals' decisions and student population type are described in this paper. Eight Sacramento area schools serving four different student populations--agricultural, military, urban, and stable--were studied. Findings indicate that a significant number of students move frequently enough to impact students, teachers, and schools. Unlike research on migrant students, little acknowledgment of student mobility and its effect on the educational system exists in current literature. Problems related to student mobility are inconsistent curricula, difficulty of student needs assessment, and the primary assignment of responsibility to teachers. Unlike migrant student research, little acknowledgment of student mobility and its effect on the educational system exists. Recommendations are made concerning patterns of student mobility, classroom strategies, teacher perceptions, and effects of student mobility on principals' decision making. Figures and tables highlight the research results. An extensive bibliography and appendices containing the survey and interview instruments are included. (LMI)