In this study we identify the number and the characteristics of the words used in letters by Primary and Secondary school EFL learners at the end of Spanish compulsory educational stages. The compositions were submitted to WordSmith Tools (Version 6.0) so as to classify the words according to alphabetic order, word frequency, statistical lists and collocation patterns in each of the courses under examination. We completed this quantitative analysis by means of a qualitative analysis of the top 50 word types for each course. Results revealed an increase in the means of words used in each educational stage, although the increase was lower than expected and practically based on substantives rather than on verbs, adjectives or adverbs. From a qualitatively perspective, we found similarities in the vocabulary used in the two courses. Nevertheless, we also observed differences that suggest the existence of idiosyncratic features at the end of each educational stage.