We study the testability implications of public versus private consumption in collective models of group consumption. The distinguishing feature of our
approach is that we start from a revealed preference characterization of collectively rational behavior.Remarkably, we find that assumptions regarding the public or private nature of specific goods do have testability implications, even if one only observes
the aggregate group consumption. In fact, these testability implications apply as soon as the analysis includes three goods and four observations. This stands in sharp contrast
with existing results that start from a differential characterization of collectively rational behavior.