This study examined differences between stable (n=107) and mobile (n=39) students attending a three-year middle school in Terre Haute (Indiana). Demographic variables of gender, ethnicity, and family income were considered, in addition to mobility, to assess possible relationships with aptitude and achievement. Achievement was measured by the Indiana Statewide Testing for Educational Progress (ISTEP) exam, given during the first half of the eighth grade. A correlation was measured between each of the demographic variables and each of the subtests of the ISTEP exam, the ISTEP battery score, and an aptitude score. A significant correlation was found between mobile students and low scores on the language subtest of the ISTEP exam. No relationships between mobility and the math or reading subtests of the exam were found, nor was there a significant correlation between mobility and total battery scores on the ISTEP. Gender was the only demographic variable that displayed a significant correlation to achievement. Aptitude, though highly correlated to achievement, did not exhibit a significant correlation to mobility or demographics. Multiple regression analysis failed to add any significance to the combined predictor variables. Four charts and three tables present the data. (Author/JLS)