I've been doing supply for ages, there needs to be flexibility in the system so schools can respond to the community they are in.
Some things I have come across that have worked in one school but might not in others.
Compulsory and free breakfast. OK no one is forced to eat but everyone is forced to go to the room where breakfast is available. It needs to be a good variety too.
Behaviour detentions done by SLT. Detention is the same day as the reason for it.
Rewards systems that reward the quiet kids who just plod on getting average to good grades not just the high flyers or the disruptive students.
Teachers to be treated as professionals, not as someone who can be replaced by a teenager or an ex squaddie.
CPD that is relevant and useful and allows teachers to follow a particular route eg SEN in mainstream
Some lessons that are not linked to GCSEs. One local school does 'enrichment' that is a series of 12 week courses in dance, martial arts, languages, art, music etc.
Better use of technology, using something like moodle effectively can cut down on marking for teachers and give instant feedback to students. I'm thinking things like drag and drop labeling of diagrams.
Homework clubs could involve tech so students can log on to a virtual classroom with a teacher to help in each subject area.