  We revisit the nature of large dips in flux from extinction by dusty
circumstellar material that is observed by Kepler for many young stars in the
Upper Sco and $\rho$ Oph star formation regions. These young, low-mass "dipper"
stars are known to have low accretion rates and primarily host moderately
evolved dusty circumstellar disks. Young low mass stars often exhibit rotating
star spots that cause quasi-periodic photometric variations. We found no
evidence for periods associated with the dips that are different from the star
spot rotation period in spectrograms constructed from the light curves. The
material causing the dips in most of these light curves must be approximately
corotating with the star. We find that disk temperatures computed at the disk
corotation radius are cool enough that dust should not sublime. Crude estimates
for stellar magnetic field strengths and accretion rates are consistent with
magnetospheric truncation near the corotation radius. Magnetospheric truncation
models can explain why the dips are associated with material near corotation
and how dusty material is lifted out of the midplane to obscure the star which
would account for the large fraction of young low mass stars that are dippers.
We propose that variations in disk orientation angle, stellar magnetic field
dipole tilt axis, and disk accretion rate are underlying parameters accounting
for differences in the dipper light curves.
