  A comparison of the hot and cool boundaries of the classical instability
strip with observations has been an important test for stellar structure and
evolution models of post- and main sequence stars. Over the last few years, the
number of pulsating pre-main sequence (PMS) stars has increased significantly:
36 PMS pulsators and candidates are known as of June 2007. This number allows
to investigate the location of the empirical PMS instability region and to
compare its boundaries to those of the classical (post- and main sequence)
instability strip. Due to the structural differences of PMS and (post-)main
sequence stars, the frequency spacings for nonradial modes will be measurably
different, thus challenging asteroseismology as a diagnostic tool.
