The eighteen-statement Attitudes Toward Mainstreaming Scale (ATMS) was cross validated through a principal axis factor analysis procedure. The 159 subjects comprising the original sample and the 164 subjects comprising the cross-validation sample included both preservice students and inservice teachers representing seventeen teaching fields. The same three factors, named Learning Capability, General Mainstreaming, and Traditional Limiting Disabilities, emerged from the analysis of each sample. Cronbach alpha reliability coefficients for the total scale were .89 and .88 for the two samples ; those for the factors ranged from .76 to .84. Pearson correlations between individual factors and total scale scores ranged from .81 to .86 with factor intercorrelations ranging from .42 to .55. These results seem to indicate that enough evidence exists concerning the reliability and factorial validity of this scale to justify the use of the ATMS in further studies of attitudes toward mainstreaming. EDUCATIONAL AND PSYCHOLOGICAL MEASUREMENT 1980,40 THE practice of &dquo;mainstreaming,&dquo; integrating disabled students into the regular classroom, is an important aspect of the implementation of the Education for All Handicapped Children Act of 1975. As the actual use of mainstreaming becomes more prevalent, it becomes increasingly important to evaluate the attitudes of those individuals intimately concerned with the process (Moore and Fine, 1978).The literature, including compilations of measurement reviews, offers no evidence that a viable scale of attitudes toward mainstreaming currently exists. In most instances, instruments used to measure atti-1 Appreciation is expressed to Alice E. Klein, who provided both general advising and editing and specific assistance with statistical procedures, and to Robert A. Hawley, who assisted with data processing.