One question I like to ask myself regularly is: What would Lean software development look like if Agile development had never happened? That thought helps to clarify some of the more dubious ideas bouncing around the Agile camp.
A Scrum team, like most Agile teams, is meant to be around 5-9 people. A key practice of Scrum, common to most Agile processes, is the daily standup meeting. The daily scrum meeting enumerates each of the team members and asks them for a brief history, a brief plan, and any obstacles. The idea is to regulate productivity and identify special cause variation. The cost of the meeting is controlled by limiting it to 15 minutes (typically). This regular n-way communication helps control some of the problems that Fred Brooks described in The Mythical Man Month. In theory, Scrum looks like a closed-loop control system with two nested feedback controllers (the daily standup, and timeboxed iteration planning). That theoretical description is what got me interested in Scrum in the first place.
One of the development teams I’m working with has got upwards of 40 people all on the same kanban board. The kanban teams I’m working with also do daily standup meetings. A daily standup with 40 people could not possibly finish in 15 minutes if everybody got their turn at status reporting. But they do finish in 15 minutes with great reliability, so they must be doing something different. The kanban process revolves around workflow first, so a natural consequence is that the standup meeting enumerates work-in-process instead of headcount. Only some of the WIP requires any comment (for special causes), and then only one or two people who are involved with that special cause really need to say anything. The board itself continuously broadcasts the productivity status of the system. Upstream resources are always on the hook for delivery to their downstream customers. Productivity lapses show up on the board very quickly and stand out like a sore thumb. Lean thinking is relentlessly value driven.
A consequence of Scrum and the “scrum of scrums” is that such a small span of control will create a deep hierarchy as you scale up. That’s not very lean. A lean organization ought to be pretty flat, and a span of control of 40 is very flat indeed.