In order to attempt to identify the linguistic difficulties of slow learners, errors made by two groups of English-speaking adults learning French as a second language were compared. The subjects of the two groups shared similar characteristics, with the exception of the amount of time required to cover the same linguistic material (Group 1: 17 weeks; Group 2: 30 weeks). To elicit oral utterances three techniques were used: (1) free expression; (2) translation; and (3) the oral part of an achievement test. Results showed that the number of errors made by slow learners increased in proportion to the degree of constraint imposed by the task, that the difference between the two groups is highly significant for the total number of verb errors, and that slow learners are much more likely than others to commit some kinds of errors. The data from the two groups are compared and interpreted from three aspects: the role of the native language, use of rules, and overgeneralization. Learner strategies are hypothesized and a few tentative suggestions are made for teaching. (Author/AMH)