PURPOSE: To compare the occurrence of altered phonological processes and to use the severity index of phonological disorder to compare speech and writing samples from dyslexic students and students with good academic performance. METHODS: Participants were 34 students of both genders from second to fifth grade, with ages between 8 years and 11 years and 11 months, divided into: G1 (17 students with interdisciplinary diagnosis of dyslexia) and G2 (17 students with good academic performance). Naming and imitation tasks (ABFW) comprising, respectively, 34 pictures and 39 words were used. Elaboration of a thematic writing was also requested, based on a logic sequence of pictures. RESULTS: Dyslexic children in this study presented lower performance than the students with good academic performance regarding, in speech, the phonological process of consonant cluster simplification (imitation task), and, in the analysis of the writing production, the criteria: unaltered cursive trace, functional dysgraphia, hyposegmentation, and correct spelling. However, the severity of phonological disorders of speech and written samples was mild in both groups. CONCLUSION: Students with dyslexia presented alterations in phonological processes and in writing, with lower performance when compared to the students with good academic performance. As for the severity index PCC-R for speech and written samples, both dyslexic students and those with good academic performance were classified as mild.