  We study the debated contribution from thermally pulsing asymptotic giant
branch (TP-AGB) stars in evolutionary population synthesis models. We
investigate the Spectral Energy Distributions (SEDs) of a sample of 51
spectroscopically confirmed, high-z ($1.3<z_{\rm spec}<2.7$), galaxies using
three evolutionary population synthesis models with strong, mild and light
TP-AGB. Our sample is the largest of spectroscopically confirmed galaxies on
which such models are tested so far. Galaxies were selected as passive, but we
model them using a variety of star formation histories in order not to be
dependent on this pre-selection.
  We find that the observed SEDs are best fitted with a significant
contribution of TP-AGB stars or with substantial dust attenuation. Without
including reddening, TP-AGB-strong models perform better and deliver solutions
consistent within $1\sigma$ from the best-fit ones in the vast majority of
cases. Including reddening, all models perform similarly. Using independent
constraints from observations in the mid- and far-IR, we show that
low/negligible dust attenuation, i.e. $E(B-V)\lesssim 0.05$ , should be
preferred for the SEDs of passively-selected galaxies. Given that TP-AGB-light
models give systematically older ages for passive galaxies, we suggest number
counts of passive galaxies at higher redshifts as a further test to
discriminate among stellar population models.
