This article reports the findings of a comparative analysis of two English teaching course book series which are widely used in school years 4-6 in Sweden: Good Stuff and New Champion. The analysis comprises comparisons of the vocabulary component in the teaching materials and examines the extent to which words -- adjectives, nouns and verbs -- recur in the books, whether there is a common core of words in the two series and, finally, whether vocabulary in the two teaching materials corresponds with accepted measures of English high-frequency words. The study shows that variation in vocabulary is considerable in individual books, within a series and between the two series; all textbooks contain a high proportion of one-time and low-frequency words. As a result, it is difficult to pin down a common core vocabulary. The study further shows that even though many words do correspond to general high-frequency words, as much as one-third are not found among the 2,000 most frequent English words.