These books provide systemic background to same-age & multi-age school systems
Chaos, Culture, and Third Millennium Schools (2000) is a first look at school management and sets the scene for vertical tutoring, introducing the idea of the upside-down school and other models
Vertical Tutoring (2010) outlines management ideas supporting VT. While this is a good basic intro you may find the later books more informative and instructional. It is a VT primer in a way.
The Systems Thinking Schools (2013) outlines the systems rationale for mixed-age groups and implementation and acts as a school systems thinking primer besides giving more detail on implementation.
From School Delusion to Design (2015) is the latest in this series and includes more of the rationale and implementation/management side of transformational change to VT including a step-by-step guide.
The Socially Collaborative School (2019) is the final book in the VT series and includes the latest research. It is also the longest book!
...available from Amazon Books
This is my local school. Despite operating in a selective catchment area, this non-selective school fought against the odds to become a really good school.
An essential part of its journey involved the introduction of vertical tutoring. The effect continues to:
improve learning relationships
make sure every child is known
increase leadership at all levels
ensure that every child is a mentor
build parent partnership
improve outcomes over time
make interventions rapid
enable information to increase & flow
make school safe & dramatically reduce bullying