While there may be something that may be innovative in theory, I'm not sure how it would play out in real life.  

Though making use of the same basic technology that emergency vehicles use to receive green lights at intersections, this technology also brings the risk of unintended consequences.  If properly synchronized, modern traffic signals are already designed to reduce travel times and times stopped at intersections; school buses (much more common than fire trucks and ambulances) would make for an extensive barrier to ensuring that signals stay synchronized.  It could possibly lead to longer travel times to school for those who do NOT ride the bus....  

As far as finding ways to improve efficiency, changes may have to be sourced elsewhere in the bus design (I have to wonder how well stop-start technology would integrate).