A professional development training I have experienced and felt it was effective was one I completed over a two-week period, conducted by our teachers' association and the Canadian teachers' federation. The theme was special education, education for all. The course exposed teachers to various strategies they could use in the classroom to reach all learners, assessment practices, identifying various disabilities children may have been it visible or invisible.  This helped me change my teaching approaches and improve my teaching styles. What was also great was the entire staff was a part of the training process.