  We employ an effective kinetic description to study the space-time dynamics
and development of transverse flow of small and large collision systems. By
combining analytical insights in the few interactions limit with numerical
simulations at higher opacity, we are able to describe the development of
transverse flow from very small to very large opacities, realised in small and
large collision systems. Surpisingly, we find that deviations between kinetic
theory and hydrodynamics persist even in the limit of very large interaction
rates, which can be attributed to the presence of the early pre-equilibrium
phase.
