supporting those changes. Accordingly, curricular content specified as important by textbook adoption policies in large states has great influence on the content of commercially available texts (Tyson, 1997).

Instructional materials are also produced by entities other than publishing companies. Federal agencies and other grant-awarding sources often support nonprofit organizations and educators at universities or school districts in producing discipline-specific instructional materials and programs. Teachers may also create some of their own materials individually and with peers, sometimes in response to school or district curriculum frameworks and sometimes based on their own views of what is important for students to learn or based on materials they encounter at professional meetings.

Teacher-support materials developed by commercial publishers or districts, designed to assist teachers as they begin to implement new programs and materials or attempt to integrate technology into their curriculum, are key elements in the curricular system. In part to address concerns about underprepared teachers, demands have increased for such materials to accompany student materials, offering support to teachers in helping them to understand what to teach and how to teach it (National Research Council [NRC], 1999e). Another consideration is the well-documented fact that the enacted curriculum is often different than the intended curriculum (Robitaille et al., 1993; NCES, 1996; Ferrini-Mundy and Schram, 1997). What teachers actually elect to teach and to whom may reflect their own interpretation of the curriculum, as well as their school and classroom environment.

Selection Mechanisms

A wide range of forces shape the processes for selecting instructional materials used in schools. These events are largely dependent on a district’s financial status and its current educational focus (NRC, 1999e). The timing of textbook adoptions is often linked to school funding cycles; the purchase of resource materials

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