Addressing recent calls for investigating the specific quality of reflection associated with the uses of portfolios in teacher education, this paper describes and interprets the "practice of portfolio construction" as revealed in the construction and presentation of two kinds of portfolio in two in-service courses for mentors of teachers in Israel: a "process" portfolio and a "product" portfolio. The study revealed that the language of practice and form of reflection bore striking similarities across the two practices of portfolio construction, regardless of their differences in content, purpose, organization and the degree of intervention of the course instructors in its construction. In both types of portfolios, the mentors described their learning mostly at technical levels of reflection. This tendency raises the question of whether the genre of portfolio writing, inevitably bound by institutional constraints, is generically conducive to reflecting on controversial experiences at interpretative, critical levels. The study suggests that within a centralized educational system, as in the case of Israel, the documentation of critical reflection is problematic.