This report evaluates a program serving high school students in Seattle (Washington) public schools who demonstrate a need for increased language-based academic assistance due to their limited English proficiency. The Mainstream Instructional Support program served 170 students at 2 high schools with 1 resource teacher and 3 instructional assistants. These instructors assisted with completing assignments, developing reading and study skills, counseling, outreach, and translating services. Staff development, materials development, and parent involvement were also important aspects of the program. The evaluation looked at both program implementation and student outcomes. The latter were measured by looking at students' academic success and other indicators of successful progress toward graduation such as attendance rates, grade point averages, and credits toward graduation. The program had no statistically significant effect in raising students' standardized test scores, grades, or attendance rates when compared with like data for students in a similar but unserved comparison group. However, narrative data, administrator and teacher responses, and other indicators suggested that the program had a significant positive impact. Data are presented in four tables. Four appendices present the following: (1) four tables of standardized change score means; (2) the graduation requirements of the Seattle Public Schools and selected study forms; (3) a list of courses attended by program staff; and (4) sample daily log reports completed by staff members. (JB)