In this paper we revisit the problem of grain growth in processing plasmas, recently reviewed by Watanabe (1997). In our model we include the effect of grain size dependence on secondary electron emission. We find that the secondary emission from the grains due to energetic -electrons from the negatively biased electrode cannot alone produce grains of opposite polarity (i.e. the smaller grains are positively charged and the larger grains are negatively charged), but could do so if additionally there is electron depletion. While electron depletion occurs in the sheath due to its negative potential, it can also occur at the sheath edge due to absorption by the large population of dust grains. Additionally, we note that even at the sheath edge stochastic heating of the smaller grains by energetic -electrons leading to stochastic thermionic emission could also lead to a small fraction of very small grains to be positive at any time.