A study examined two high school English teachers' explorations of portfolio assessment and the effect of these explorations on their teaching and on students' understandings of their own learning and knowledge. The teachers (one with 28 years of experience, the other with 3 years teaching experience) taught at a public city school with an ethnically and economically diverse student population. The teachers selected their ninth-grade average-track classes for study. Four focus students in each class represented a range of talents and abilities. Data included field notes of classroom observations, transcripts of interviews with teachers and students, and the content of the students' portfolios. Results indicated that: (1) the veteran teacher worked to instill students with the discipline necessary to stay with the text rather than drift into personal connections with it, while the new teacher created a supportive learning community where students could share their responses to texts; (2) the veteran teacher emphasized polishing up finished products and completing academic tasks, while the new teacher integrated portfolio activities into ongoing classroom activities; and (3) the veteran teacher was disappointed from the beginning in the quality of the students' portfolio collections, while the new teacher was satisfied and excited about her portfolio experience yet in doubt that her efforts would have any school-wide impact. Findings suggest that enacting assessment reform is difficult and often discouraging, for educators are called to question long-held beliefs of the nature of teaching and learning. (RS)