Transformation from a same-age (linear) system to a multi-age, non-linear system needs considerable reflection and care. It is easy to make big mistakes. You cannot use the hand-me-down thinking behind the existing horizontal model to create a vertical system. So much is counterintuitive and so much has to be unlearned. There are schools that have ignored training and reverted back to their old model. This is simply poor leadership and a lack of openness to unlearning, not a system fault.
This short video is about change and is sometimes used in training, It deals with the 'why' but not the 'how'. That's why external guidance is important.
This is how Robin Cox, N.Z based educator, describes the importance of the multi-age tutor system. Simply press the button