The investigation of T Tauri stars and their interaction with their circumstellar matter using CoRoT data revealed the existence of a new class, the AA Tauri type objects. Previously to the CoRoT observations, T Tauri stars were known to either show sinusoidal light variations that are caused by spots on the stellar surface, or completely irregular variability that is caused by the gas and dust disks surrounding the young stars. AA Tauri type objects show periodically occurring minima that are different in depth and width, hence are semi-regular variables. With the CoRoT observations this class of objects could be established. Exciting insights into the earliest phases of stellar evolution also come from the comparison of the variability present in the optical light to that in the infrared and the X-ray regime.