  We study the evolution of the scaling relations between maximum circular
velocity, stellar mass and optical half-light radius of star-forming
disk-dominated galaxies in the context of LCDM-based galaxy formation models.
Using data from the literature combined with new data from the DEEP2 and AEGIS
surveys we show that there is a consistent observational and theoretical
picture for the evolution of these scaling relations from z\sim 2 to z=0. The
evolution of the observed stellar scaling relations is weaker than that of the
virial scaling relations of dark matter haloes, which can be reproduced, both
qualitatively and quantitatively, with a simple, cosmologically-motivated model
for disk evolution inside growing NFW dark matter haloes. In this model optical
half-light radii are smaller, both at fixed stellar mass and maximum circular
velocity, at higher redshifts. This model also predicts that the scaling
relations between baryonic quantities evolve even more weakly than the
corresponding stellar relations. We emphasize, though, that this weak evolution
does not imply that individual galaxies evolve weakly. On the contrary,
individual galaxies grow strongly in mass, size and velocity, but in such a way
that they move largely along the scaling relations. Finally, recent
observations have claimed surprisingly large sizes for a number of star-forming
disk galaxies at z \sim 2, which has caused some authors to suggest that high
redshift disk galaxies have abnormally high spin parameters. However, we argue
that the disk scale lengths in question have been systematically overestimated
by a factor \sim 2, and that there is an offset of a factor \sim 1.4 between
H\alpha sizes and optical sizes. Taking these effects into account, there is no
indication that star forming galaxies at high redshifts (z\sim 2) have
abnormally high spin parameters.
