Despite intensive efforts, our understanding of the cell cycle exit of neuronal progenitors in the developing cerebellum is incomplete. It is important to understand this process, as disruption in cell cycle exit can be linked to cancers, such as the most common malignant pediatric brain tumor, medulloblastoma. One of the main cell types thought to give rise to medulloblastoma is cerebellar granule cell progenitors, or GCPs. GCPs give rise to cerebellar neurons, which interact with Purkinje cells, the principal output neuron of the cerebellar cortex, and they are essential for cerebellar architecture. GCPs exit the cell cycle after birth in mice and can be purified to near homogeneity, offering a robust model for studying cell cycle exit. We adapted a protocol from the Hatten laboratory for purification of GCPs, followed by plating on laminin coated plates. We then isolated GCPs at distinct time points to assess cell cycle exit parameters. To determine the transcriptional profiles of GCPs that are cycling, differentiating, or differentiated, we performed RNA-sequencing at individual time points. We performed time series analysis of all transcripts and identified times and pathways associated with cell proliferation, cell cycle exit, and neuronal differentiation. Here, we provide detailed methods for analyzing GCP cell proliferation and differentiation in vitro and how to use this information for determining cell cycle exit parameters and pathways.