In 2015 the US National Research Council — part of the National Academies — published a review pulling together decades of empirical research on what makes teams effective. Its central conclusion is stated without hedging:

"Team processes are the primary leverage point for enhancing team effectiveness."

Many leaders I work with are a bit stuck on composition. You inherit a team. Hiring is slow, expensive and constrained. Moving people is disruptive and often politically impossible. If team quality were mostly a function of who's in the room, most leaders would have very little room to move.

This research says the strongest lever is not composition but process — how the team actually works. And process is the one thing a leader can start changing immediately, without a requisition or a restructure.

Strongest for interdependent teams

The review also pins down something I'd put in front of any executive team.

The process relationship with performance was more than twice as strong where a team's work was highly interdependent as where it wasn't.

Which describes most knowledge work. Most project delivery. And virtually every senior leadership team, where nothing significant gets done by one person acting alone.

Other findings

Two other properties of the team layer were solidly related to team performance: shared mental models and transactive memory — a team's shared understanding of the work, and its sense of who knows what — and team efficacy, a team's belief in its own capability.

And the review identifies three routes to influencing team process: team composition, team leadership, and team professional development. Note that composition is still on the list. The finding isn't that who's in the team is irrelevant; it's that process is where the primary leverage sits.