Agile started at the team level. Both Scrum and eXtreme Programming were designed for and built around single teams. Scale back in 2004 meant three teams working together. So what do we mean by mid-scale? A company that has 500 people in technology with highly interdependent teams may be much tougher to implement than a company twice the size but with less dependent teams.
We prefer to define small, mid and large scale by the dynamics present:
Dynamics of scale
There are several factors that affect the difficulties of changing an organization:
There is not a well-defined line from small to medium to large scale. The picture below depicts how the size of an organization alone does not define the scale involved.
Why scale matters
The scale of an organization will affect the approach one takes.
At small scale it is simple enough to start all of the teams doing some team-level approach such as Scrum, Kanban, XP, or Team Agility. Everyone can be trained at the same time and pretty much work in the same manner.
Mid-scale requires more effort but a principle based approach using well-defined steps that result in an emergent method can be used. If the size of the organization being transformed is more than 125 people (Dunbar’s number) then it is likely that working on groups up to 125 people at a time is best.
Large-scale may require a predefined approach to get started. However, staying with the well-defined approach will almost certainly lead to stagnation as no one-sized fits all.