This study examined the scores on a state standards-based Grade 5 Science assessment obtained by a group of students without learning disabilities who took the standard form of the test and by three groups of students with learning disabilities: one taking the standard form of the test without accommodations or modifications, a second taking the test with accommodations, and a third group taking the test with modifications. The groups received accommodations or modifications that were specified in their 504 or IEP plans. Unlimited time was granted to complete the test. A series of item-level, then parcel-level, exploratory and confirmatory factor analyses investigated whether or not the assessment demonstrated factorial invariance for the four groups of students studied. The results of this study help substantiate the validity of test scores for students with disabilities who take the test with the particular set of accommodations or modifications that were used in this study. In addition, the results lend support to modifying this state's policy in order to aggregate scores obtained by students without learning disabilities and by students with learning disabilities who have taken the assessment with accommodations or modifications required by their 504 plans or IEPs for AYP purposes. Appended are: (1) Observed Reporting Strand Intercorrelation Matrices by Group Adjusted for Attenuation; (2) Parcel-Covariance Matrices; (3) Summary of Parcel-Level Exploratory Factor Analyses by Group; and (4) Summary of Factor Loadings and Residuals From Final Parcel-Level Multi-Group Confirmatory Factor Analyses. (Contains 26 tables, 4 figures and 17 notes.)