Practicality is the "Achilles heel" of alternative assessment in middle school science. This 5-year study of an "early adopter" school explores factors that enable alternate assessment to thrive in spite of practical problems. Interviews with five seventh-grade life science teachers and five eighth-grade physical science teachers who initiated and continue to sustain new assessment methods indicate that in the early years they explored many approaches, and were not blamed for problems. Since many aspects worked well, the teachers were convinced by their own experience of students' increased ability to understand and explain science concepts. A collegial atmosphere and administrative support in time and resources helped to sustain the innovation. (Contains 3 figures and 12 references.) (Author/SLD)