This paper provides a new methodology for the diachronic study of new firm growth, theoretically grounded in the work of Penrose (1995). We show that a model of firm growth as an unfolding process makes possible draw simple, measurable inferences from firm level to aggregate evidence on growth paths of new firms, expressed as propositions. Metrics on growth paths of new firms in three longitudinal samples of new firms are examined for evidence at the aggregate level consistent with the dynamic model. Dynamic processes in the early development of young firms result in variations in the timing, magnitude, duration and rate of change of growth as between firms and in the same firm over time. The conceptual and methodological framework in this paper provides a basis for future research aimed at explaining the development of new firms