  We have discovered T Tauri stars which show startling spectral variability
between observations seperated by 20 years. In spectra published by Bouvier &
Appenzeller (1992) these objects showed very weak H-alpha emission, broad CaII
absorption and so called ``composite spectra'', where the spectral type
inferred from the blue region is earlier than that inferred from the red. We
present here new spectroscopy which shows that all four stars now exhibit
strong H-alpha emission, narrow CaII emission and a spectral type which is
consistent at all wavelengths.
  We propose a scheme to understand these changes whereby the composite spectra
of these stars can be explained by a period of active accretion onto the
central, young star. In this scheme the composite spectrum consists of a
contribution from the stellar photosphere and a contribution from a hot,
optically thick, accretion component. The optically thick nature of the
accretion flow explains the weakness of the H-alpha emission during this phase.
Within this scheme, the change to a single spectral type at all wavelengths and
emergence of strong H-alpha emission are consistent with the accretion columns
becoming optically thin, as the accretion rate drops. There is a strong analogy
here with the dwarf novae class of interacting binaries, which show similar
behaviour during the decline from outbursts of high mass-transfer rate.
  The most important consequence of this interpretation is that these objects
bring into question the association of Weak-Line T Tauri stars (WTTs) with
non-accreting or discless objects. In light of this result we consider the
justification for this paradigm.
