This paper examines the relationship between rural female literacy and the size of the child population (0-6 years) using block level data from the population census of 1991 for West Bengal. Its purpose is to find out if there is any threshold level of female literacy associated with a rapid decline in the size of the under-6 population. The analysis is done separately for three social groups; the tribals, the scheduled castes and the rest or the 'general' population. The results have an important bearing on policy while processes behind these are of considerable significance to researchers. Further validation of these patterns using 2001 Census data and similar analysis for states is indicated.