  We present new ATCA observations at 3.3 mm of 27 young stellar objects in the
rho-Oph young cluster. 25 of these sources have been detected. We analyze the
sub-millimeter and millimeter SED for a subsample of 17 isolated class II
protoplanetary disks and derive constraints on the grain growth and total dust
mass in the disk outer regions. All the disks in our sample show a mm slope of
the SED which is significantly shallower than the one observed for the ISM at
these long wavelengths. This indicates that 1) class II disks in Ophiuchus host
grains grown to mm/cm-sizes in their outer regions, 2) formation of mm/cm-sized
pebbles is a fast process and 3) a mechanism halting or slowing down the inward
radial drift of solid particles is required to explain the data. These findings
are consistent with previous results in other star forming regions. We compare
the dust properties of this sample with those of a uniformly selected sample in
Taurus-Auriga and find no statistical evidence of any difference in terms of
grain growth between the two regions. Finally, in our sample the mm slope of
the SED is not found to correlate with indicators of grain growth to micron
sizes in the surface layers of the inner disk.
