A discussion of English-as-a-Second-Language (ESL) instruction in the mainstream classroom focuses on teacher training needs to meet the educational needs of limited-English-proficient (LEP) students. After a brief analysis of the teacher's role in relation to the development of all students, and in particular to the language development of LEP students, a teacher development project linking theory and practice is described. A group of teachers met to discuss the diverse needs of this population and visited a school in which students had been exposed to some ESL activities by a visiting specialist. During one school term, teachers created a program of both free and directed classroom activities that promote English language use and student interaction with both peers and teachers, with the objective of providing opportunities to observe student language behavior. Teachers were also provided with pre-reading materials and taught the use of cooperative learning techniques by a specialist. During the following term, the techniques were implemented in the classrooms. As a result, the teachers saw changes in their ability to observe students and reflect on their own teaching practices, invited parent involvement, became more confident, and developed guidelines for supporting each other in effective teaching. (MSE)