Efforts at one high school to reconsider its practices of ability grouping and explore alternative assessment and grouping practices are described. Assessment of the schools' practices found that students in lower ability groups had a less stimulating curriculum, fewer positive role models, lower motivation, lower expectations for themselves, and worked with teachers who also held lower expectations for them. When mobility did take place between ability levels, it was more often downward than upward. The use of national standardized placement tests was replaced by teacher-designed, criterion-referenced assessment tools, resulting in significantly different balances of placements. A pilot program was launched to replace a remedial composition course with participation in regular level classes supplemented by ongoing lunch hour tutoring in composition, resulting in improved grades for participants. The success of this program led the school to eliminate lower ability levels in other content areas, and to modify curriculum in remaining lower-level courses. A variety of modifications were implemented to support heterogeneous grouping, including expanded use of cooperative learning and classroom workshops. Staff development is seen as essential to the future of these modifications. (PB)