The purpose of the study was to compare the basic skills achievement scores of mobile and non-mobile students within the Portland Public Schools. The problem was to assess the effect of this mobility on basic skills achievement and the total educational program. The study was designed to test differences in reading, language usage and mathematics achievement test scores between pupils in the third through the eighth grades. The instrument that was used was the Portland Achievement Levels Tests of reading, language usage and math. These tests are administered to students in grades 3 - 8 in the fall and spring of each school year. A questionnaire was also designed to determine the effect of student mobility on instructional programs. This questionnaire was mailed to 81 principals with 56 responding. The Portland Public Schools computer banks were utilized to plot the basic skills test results for two groups of students: 1. The clear and intact group, which was the student who was in the same school from September through June (grades 3 - 8). 2. The mobile student (grades 3 - 8) who had a valid fall and spring test score, but from different schools. Plotting was done for the residual effect of variables in basic skill gains rather than plotting for the effects of regression. Additional analysis took place using multiple regressions by stability index, to determine the relationship between student achievement test scores and the independent variables of mobility and other independent variables (ethnic groups, gender). It was determined that student mobility and the independent variables of gender and ethnicity had no negative effect on basic skills achievement test scores. However, for the stable student, the higher the school stability index, the higher the achievement level for the non-mobile students in that school for the fall testing. The achievement gain was no different for a student in a high stability school versus a low stability school. Additionally, based on the results of the questionnaire used in the study, most principals felt that student mobility had a negative impact on instructional programs. Most of the responding principals, however, were opposed to a more structured district wide basic skills curriculum as a way of moderating the negative effects of student mobility on the educational program. Student mobility is a factor related to the success of a school academic program. It cannot, however, be taken as an answer to the low achievement of mobile students. This study concludes that all students can achieve academically, regardless of their mobility. Recommendations were made to the Portland School District that in order to facilitate and decrease the problem of student mobility, the district might wish to require that each school have a formal plan for integrating new students into the instructional program. Additionally, a more structured district wide basic skills curriculum was recommended. Suggestions for additional in-depth studies were made to determine the kinds of problems that students and school staffs encounter with school mobility. This would include a longitudinal study for students with only one valid test score during an academic year, comparing their fall or spring scores over several years and the frequency of their mobility.