Rhabdomyosarcoma is a pediatric malignancy thought to arise from the uncontrolled proliferation of myogenic cells. Here, we have generated models of rhabdomyosarcoma in the zebrafish by inducing oncogenic KRASG12D expression at different stages during muscle development. Several zebrafish promoters were used including the cdh15 and rag2 promoters that drive gene expression in early muscle progenitors, and the mylz2 promoter that expresses in differentiating myoblasts. The tumors that developed differed in their ability to recapitulate normal myogenesis. cdh15:KRASG12D and rag2:KRASG12D fish developed tumors that displayed an inability to fully undergo muscle differentiation by histologic appearance and gene expression analyses. In contrast, mylz2:KRASG12D tumors more closely resembled mature skeletal muscle and were most similar to well-differentiated human rhabdomyosarcoma by gene expression. mylz2:KRASG12D fish showed significantly improved survival compared to cdh15:KRASG12D and rag2:KRASG12D fish. Tumor-propagating activity was enriched in myf5-expressing cell populations within all of the tumor types. Our results demonstrate that oncogene expression at different stages during muscle development has profound effects on the ability of tumor cells to recapitulate normal myogenesis, altering the tumorigenic capability of these cells.