  The evolution of AGB stars is notoriously complex. The confrontation of AGB
population models with observed stellar populations is a useful alternative to
the detailed study of individual stars in efforts to converge towards a
reliable evolution theory. I review here the impact of studies of star clusters
on AGB models and AGB population synthesis, deliberately leaving out any more
complex stellar populations. Over the last 10 years, despite much effort, the
absolute uncertainties in the predictions of the light emitted by intermediate
age populations have not been reduced to a satisfactory level. Observational
sample definitions, as well as the combination of the natural variance in AGB
properties with small number statistics, are largely responsible for this
situation. There is hope that the constraints may soon become strong enough,
thanks to large unbiased surveys of star clusters, resolved colour-magnitude
diagrams, and new analysis methods that can account for the stochastic nature
of AGB populations in clusters.
