all PMS achieve these short rotation periods (See for example @Herbst.02 for observations of the $\sim 1$ Myr Orion Nebula Cluster, @Cieza.06 for observations of $\sim 2-3$ Myr IC 348, @Lamm.05 for observations of $\sim 2-4$ Myr NGC 2264, @Irwin.08b for observations of $\sim 5$ Myr NGC 2362, and @Irwin.08a for observations of $\sim 40$ Myr NGC 2547). Possible explanations for the presence of slow rotators in these clusters include magnetic locking of the star’s rotation to the inner accretion disk [@Konigl.91; @Shu.94] or the presence of an accretion-driven wind which carries angular momentum away from the star [@Shu.00].

Photometric determinations of rotation periods have been obtained for stars in a number of clusters in the age range $50-200$ Myr; at these ages solar-like stars have settled on to the main sequence. Clusters that have been studied include IC 2391 [$\sim 50~{\rm Myr}$; @Patten.96], IC 2602 [$\sim 50~{\rm Myr}$; @Barnes.99], $\alpha$ Persei [$\sim 80~{\rm Myr}$; @Stauffer.85; @Stauffer.89; @Prosser.91a; @Prosser.93a; @Prosser.93b; @ODell.93; @ODell.94; @Prosser.95; @ODell.96; @Allain.96; @Martin.97; @Prosser.98a; @Prosser.98b; @Barnes.98a], the Pleiades [$\sim 125~{\rm Myr}$; @Magnitskii.87; @Stauffer.87a; @VanLeeuwen.87; @Prosser.93a; @Prosser.93b; @Prosser.95; @Krishnamurthi.98; @Terndrup.99; @Scholz.04], NGC 2516 [$\sim 150~{\rm Myr}$; @Irwin.07], and M34 [$\sim 200~{\rm Myr}$; @Barnes.03; @Irwin.06].

The data for older 