We've been working with schools to develop a "curriculum map" of big ideas of sustainability (e.g. diversity, interdependence, cycles).  Over the years we've seen that these big ideas emerge from the standards and grade expectations, school or district curricula, and teachers' passions and student interest. 

Even with in the same district schools may decide to have a different sequence of big ideas but what is critical is that the school community works on developing this together.  We have several examples from schools we've worked with here.