There is growing evidence that corrective input for grammatical
errors
is widely available to children (Farrar, 1992; Morgan, Bonamo &
Travis, 1995). However, controversy still exists concerning the extent
to
which children can identify and exploit available negative input. In
particular, very little is yet known about the longer-term effects of
negative input. Performing a time series analysis on observational data,
Morgan et al. (1995) conclude that corrective recasts are not
related to
future improvements in grammaticality. It is argued here, though, that
the data sets analysed in this study are inherently ill-suited to the
demands of time series analyses. The present study adopts an experimental
approach in order to compare the effects of negative evidence
versus positive input on the acquisition of irregular past tense verb
forms. Twenty-six children (mean age 3;10) participated in a within-subjects
design over a period of five weeks. It was found that improvements
in the grammaticality of child speech were considerably greater in
cases where negative evidence had been provided. Moreover, children's
intuitions concerning the status of irregular and overregularized forms
more closely approximated adult intuitions when corrective input was
available.