No previous research has employed learning environments criteria in evaluating the effectiveness of the system of teacher certification sponsored by the National Board for Professional Teaching Standards. Because the litmus test of any professional development effort is the extent of the changes in teaching behaviours in participating teachers' classrooms, our study drew on the field of learning environments in evaluating the effectiveness of National Board Certified (NBC) teachers in terms of their students' perceptions of their classroom environments. A sample of 443 students in 21 Grade 8 and 10 science classes taught by NBC teachers in South Florida was compared with a matched group of 484 students in 17 classes taught by non-NBC teachers in terms of classroom environment (as assessed by the What Is Happening In this Class?) and students' attitudes and achievement. Statistically significant differences (with small to medium effect sizes ranging from 0.14 to 0.35 standard deviations) were found in favour of NBC teachers for numerous classroom and environment scales (Teacher Support, Involvement, Task Orientation, Investigation and Cooperation) and for student attitudes.