Learning to read is a complex process and necessitates continuity in the school environment -- the factor of primary concern in this study. Three objectives are noted: (1) to determine differences in reading achievement between fifth grade pupils who have been in the same school since the third grade (non-mobile), and those fifth grade pupils who enter the school any time after the third grade (mobile); (2) to determine differences in the percentage of non-mobile and mobile pupils achieving at or above grade norm; and, (3) to determine if the differences are present regardless of ethnicity and socioeconomic background. Results obtained from scores on the Reading Metropolitan Achievement Tests indicate that there is higher reading achievement in non-mobile pupils, as compared with mobile pupils. A higher percentage of non-mobile pupils are reading at or above grade norm than the mobile pupils. Both findings apply to both Title I and non-Title I districts, but the magnitude of the mean difference in favor of the non-mobile group is greater for the non-Title I districts. All mean and percentage differences are statistically significant. (Author/AM)