We model a public goods game with groups, position uncertainty, and observational
learning. Contributions are simultaneous within groups, but groups play sequentially based on their observation of an incomplete sample of past contributions.
We show that full cooperation between and within groups is possible with self-interested players on a fixed horizon. Position uncertainty implies the existence of an equilibrium where groups of players conditionally cooperate in the hope of influencing further groups. Conditional cooperation implies that each group member is pivotal, so that efficient simultaneous provision within groups is an equilibrium.