Young M dwarf stars exhibit strong particle acceleration in their corona, as we can see from their bright quiescent, nonthermal radio emission. However, the mechanism for this acceleration is not well understood. Variations in the size and orientation of their radio coronae may shed new insights on the nature of their coronal activity. I will be presenting the results of a study measuring the diameters and flux densities of five M dwarf stars, using data collected by the Very Long Baseline Array (VLBA) for the Radio Interferometric Planet Search (RIPL) project. Each star was observed at 8.4 GHz in multiple epochs with 2.5 to 3 hours total time on source per observation. We measured the size of each epoch by fitting an elliptical gaussian to the visibility data. Young M dwarfs are frequently resolved but not always, and both size and orientation vary over time. Marginally resolved observations imply source sizes of multiple stellar diameters.