Purpose: to compare vocabulary performances and verify the lexical competence of students with and without difficulties learning to read and write. Methods: 93 first-grade students were divided into Group I (50 students without difficulties) and Group II (43 students with difficulties learning to read and write). They were administered the Child Language Test focusing on vocabulary. The analysis considered aspects of usual word designation, non-designation, and substitution process. The data analysis was conducted with the Mann-Whitney test, with a p-value ≤ 0.05. Results: there were significant performances in the comparison between the groups in all the conceptual fields analyzed. There was no significance for either group regarding the conceptual fields of Foods, Furniture and Appliances, Places, and Professions in non-designation; regarding Means of Transportation in substitution processes; regarding Toys and Musical Instruments in both non-designation and substitution processes. Group I had higher means than Group II in usual word designation, and lower ones in non-designation and substitution processes. Conclusion: students with difficulties learning to read and write had greater difficulties in usual word designation, as well as higher error indexes in substitution processes and non-designation, which reveals a deficient vocabulary concerning lexical access in comparison with students without difficulties.