The simultaneous X-ray and optical observations with excellent time resolution of T Tauri stars with disks may provide insight on the accretion process and the properties of the inner disk. This was one of the motivations of the CSI 2264 campaign. In this talk I will show the results obtained from time resolved X-ray spectral analysis from deep Chandra/ACIS-I observations during the optical dips and accretion bursts isolated in the CoRoT light curves of the disk-bearing members of NGC 2264. These simultaneous Chandra-CoRoT data allow us to find evidence of increasing X-ray absorption during the optical dips, to study the composition of the material responsible for the variable extinction in these stars with disks, and to find evidence for soft X-ray emission observed during the optical bursts, and thus related to the accretion process
