  We examine the early angular momentum history of stars in young clusters via
197 photometric periods in fields flanking the Orion Nebula Cluster (ONC), 81
photometric periods in NGC 2264, and 202 measurements of v sin i in the ONC
itself. We show that PMS stars spanning an age range from 0.1 to 3 Myr do not
appear to conserve stellar angular momentum as they evolve down their
convective tracks, but instead preserve the same range of periods even though
they have contracted by about a factor of three. This result seems to require a
mechanism that regulates the angular velocities of young stars. We discuss
several candidate mechanisms. The most plausible appears to be disk-locking,
though most of our stars do not have (I-K) excesses suggestive of disks.
However, a decisive test of this hypothesis requires a more sensitive
diagnostic than the (I-K) excesses used here.
