Megan Ansdell (IfA-Manoa) Young M dwarf "dipper" stars in Upper Sco and Á Ophiuchus observed by K2 We present ten young, late-K and M dwarf stars observed in K2 Campaign Field 2 that host protoplanetary disks and exhibit quasi-periodic or aperiodic dimming events. Their optical light curves show ~10-20 dips over the 80-day observing campaign with durations of ~0.5-2 days and depths of up to ~30%. These stars are all members of the ñ Ophiucus (~1 Myr) or Upper Scorpius (~10 Myr) star-forming regions. To investigate the nature of these `dippers' we obtained optical and near-infrared spectra to determine stellar properties and identify accretion signatures; adaptive optics imaging to search for close companions that could cause optical variations and/or influence disk evolution; and millimeter-wavelength observations to constrain disk dust and gas masses. Our spectra reveal Li absorption and Há emission that indicate stellar youth (<50 Myr), but also accretion rates spanning those of classical and weak-line T Tauri stars. Infrared excesses are consistent with protoplanetary disks extending to within ~10 stellar radii in most cases; however, our sub-mm observations imply low disk masses that are an order of magnitude below those of typical protoplanetary disks. We find a positive correlation between dip depth and WISE-2 mid-infrared excess, which we interpret as evidence that the dipper phenomenon is related to the inner disk near the co-rotation radius. We consider three physical mechanisms: inner disk warps caused by interactions between accretion disks and inclined magnetospheres; vortices at inner disk edges produced by Rossby Wave Instabilities; and clumps of circumstellar material related to planetesimal formation.