In Chapter 4 of "The Global Achievement Gap" Wagner takes a look at the way that teachers are trained and supported. Historically our credential programs have provided only basic teaching knowledge of and skills. The traditional student-teaching model is based on a sink-or-swim paradigm where the new teacher has to just jump into the classroom and figure it out on their own. Once you have that teaching job, there is very little opportunity for feedback or growth because teachers are essentially isolated in their classrooms.
This is really too bad, because I have very much enjoyed my training in the co-teacher model. I have been working closely with my cooperating teacher to develop lessons, learn about teaching practices that work and don't work, and receive direct feedback on my own teaching. We have a routine of frequent reflection where we look back at lessons from the week and talk about (and document) how things went and what might be improved. In this way we both get to benefit from having another in the classroom, not just in terms of immediate feedback, but also advice and recommendations for improving these lessons in the future.
It sounds as if this is not the kind of thing that will be commonplace once I get my own classroom, and that's too bad. Having two professionals in the classroom also benefits the students since we can provide more direct assistance and feedback to them. Wagner's ideas about "learning walks" where educators spend time observing other classrooms, and then discussing what is seen, sounds to me like a brilliant idea. In my previous career I was always able to collaborate with my coworkers, bounce ideas off each other and constantly try to improve my own work. It seems so unusual that this is not the case for teachers. You would think that they would all want to strive for the best learning environment and to hone their craft. This part of the culture of teaching profession is certainly a disappointment. Hopefully we can change that as more inspired teachers push for improvements and better support.