In most schools, especially urban high schools, teachers are colleagues in name only. Some schools, however, do foster substantial collegial relationships among teachers; and when schools are organized to support such teacher collaboration, the benefits are substantial. To make teacher collaboration possible and effective, two fundamental conditions appear to be crucial: interdependence and opportunity. Since teachers' main motivation and rewards are in the work of teaching, the extent that they find themselves interdependent with one another to manage and reap the rewards of teaching make joint work a worthwhile investment of time and other resources. Joint action, however, will not occur where it is prohibitively costly in organizational, political, or personal terms; school policy must support the effort, and the value placed on shared work must be stated and demonstrated. Helping teacher collaboration to work requires endorsements and rewards for collaborative efforts, school-level reorganization into teams to stimulate cooperative work, the willingness to give latitude to teachers for influence on matters of curriculum and instruction, enough time for planning periods and implementation, training and assistance, and the support of quality materials and equipment. (Contains seven references.) (GLR)