Federal policy on alternate assessment based on modified academic achievement standards (AA-MAS) inspired this research. Specifically, an experimental study was conducted to determine whether tests composed of modified items would have the same level of reliability as tests composed of original items, and whether these modified items helped reduce the performance gap between AA-MAS eligible and ineligible students. Three groups of eighth-grade students (N = 755) defined by eligibility and disability status took original and modified versions of reading and mathematics tests. In a third condition, the students were provided limited reading support along with the modified items. Changes in reliability across groups and conditions for both the reading and mathematics tests were determined to be minimal. Mean item difficulties within the Rasch model were shown to decrease more for students who would be eligible for the AA-MAS than for non-eligible groups, revealing evidence of differential boost. Exploratory analyses indicated that shortening the question stem may be a highly effective modification, and that adding graphics to reading items may be a poor modification. (Contains 5 tables and 4 footnotes.)