  We present spectral energy distribution (SED) modeling of 338 disks around T
Tauri stars from eleven star-forming regions, ranging from $\sim$0.5 to 10 Myr
old. The disk masses we infer from our SED models are typically greater than
those reported from (sub)mm surveys by a factor of 1.5-5, with the discrepancy
being generally higher for the more massive disks. Masses derived from (sub)mm
fluxes rely on the assumption that the disks are optically thin at all
millimeter wavelengths, which may cause the disk masses to be underestimated
since the observed flux is not sensitive to the whole mass in the disk; SED
models do not make this assumption and thus yield higher masses. Disks with
more absorbing material should be optically thicker at a given wavelength;
which could lead to a larger discrepancy for disks around massive stars when
the disk temperature is scaled by the stellar luminosity. We also compare the
disk masses and degree of dust settling across the different star-forming
regions and find that disks in younger regions have more massive disks than
disks in older regions, but a similar degree of dust settling. Together, these
results offer potential partial solutions to the "missing" mass problem: disks
around T Tauri stars may indeed have enough material to form planetary systems,
though previous studies have underestimated the mass by assuming the disks to
be optically thin; these planetary systems may also form earlier than
previously theorized since significant dust evolution (i.e., settling) is
already apparent in young disks.
