In this paper we employ an additive semiparametric partially linear model to uncover the way that initial output and schooling levels affect growth rates. Our results based on marginal integration allow for graphical representation of the non-linearities that characterize the effects that these variables have on growth rates and suggest the presence of multiple regimes (equilibria). Our findings seem to be in agreement with those of Durlauf and Johnson (1995) and Hansen (1996) who used a different data set.