The purpose of this research was to determine the number of distinct words in printed school English. A detailed analysis was done of a 7,260 word sample from the Carroll, Davies and Richman, Word Frequency Book. Projecting from this sample to the total vocabulary of school English, our best estimate is that there are about 88,500 distinct words. Furthermore, for every word a child learns, we estimate that there are an average of one to three additional related words that should also be understandable to the child, the exact number depending on how well the child is able to utilize context and morphology to induce meanings. Based on our analysis, a reconcilation of estimates of children's vocabulary size was undertaken, which showed that the extreme divergence in estimates is due mainly to the definition of "word" adopted. Our findings indicate that even the most ruthlessly systematic direct vocabulary instruction could neither account for a significant proportion of all the words children actually learn, nor cover more than a modest proportion of the words they will encounter in school reading materials.