In an attempt to identify effective instructional approaches, teachers were videotaped while teaching remedial mathematics. Teacher behaviors were coded and student achievement scores analyzed. Eight categories were found which distinguished between effective and ineffective teachers, including: instruction for the whole class simultaneously rather than individualized or small group work; review of seatwork with immediate feedback; use of questions rather than statements; use of questions that require students to perform rather than explain; neutral responses rather than praising or critical ones to student answers; monitoring to provide continuous feedback; and use of the majority of class time for instruction. Teachers from another group who were taught to incorporate these guidelines were found to have students with greater mathematics achievement. (CL)