  Binary black holes may form both through isolated binary evolution and
through dynamical interactions in dense stellar environments. The formation
channel leaves an imprint on the alignment between the black hole spins and the
orbital angular momentum. Gravitational waves from these systems directly
encode information about the spin--orbit misalignment angles, allowing them to
be (weakly) constrained. Identifying sub-populations of spinning binary black
holes will inform us about compact binary formation and evolution. We simulate
a mixed population of binary black holes with spin--orbit misalignments
modelled under a range of assumptions. We then develop a hierarchical analysis
and apply it to mock gravitational-wave observations of these populations.
Assuming a population with dimensionless spin magnitudes of $\chi = 0.7$, we
show that tens of observations will make it possible to distinguish the
presence of subpopulations of coalescing binary black holes based on their spin
orientations. With $100$ observations it will be possible to infer the relative
fraction of coalescing binary black holes with isotropic spin directions
(corresponding to dynamical formation in our models) with a fractional
uncertainty of $\sim 40\%$. Meanwhile, only $\sim 5$ observations are
sufficient to distinguish between extreme models---all binary black holes
either having exactly aligned spins or isotropic spin directions.
