  We revisit the published analyses of ROSAT X-ray observations of the star
forming regions NGC 2264 and Chamaeleon I (~3 and ~5 Myr old respectively) in
the light of newly published optical data. At odds with previous results on
Chamaeleon I members, we find that low mass stars in both regions have
near-saturated emission levels. Similarly to what previously found in the Orion
Nebula Cluster, Weak Line T-Tauri Stars in NGC 2264 and in the Chamaeleon I
cloud have higher X-ray activity levels respect to Classical T Tauri Stars,
arguing in favor of a role of the disk and/or accretion in determining X-ray
emission.
