I don't think this is really a worry in Australia at least. Often teachers are left coming up with lesson plans on the fly and the students suffer.

My partner is studying to become a primary school teacher and one thing that has surprised me is the level of duplication in the system. At an individual school a couple of teachers teaching the same year level are coming up with a lesson plan. There are hundreds of other schools essentially teaching to the same framework. Now I'm not advocating a completely standardised curriculum with no room for the teacher to put their own individual style in the lessons. What I am saying though is that I think everyone would benefit if there was much more sharing of knowledge throughout the system. Something like this site enables that knowledge sharing.