Objective: The goal of the study was to identify a group of adolescent “slow readers” and retrospectively test which ADHD symptoms and neuropsychological processes were affected at 8 years of age. Method: Participants (n = 670) were drawn from the Quebec Newborn Twin Study (QNTS), a longitudinal birth cohort of more than 1000 twins born between 1995 and 1998 in the greater Montreal area, Canada. Participants were tested on reading measures, ADHD symptoms, verbal and non-verbal abilities (vocabulary and block design) when they were between 14 and 15 years old. Readers who spent more than 180 seconds to read the Alouette-R test were classified as slow readers (n = 46). The slow readers were compared to the other readers on reading abilities, ADHD symptoms and neuropsychological processes (rapid naming, phonological memory, phonological analysis, temporal processing) at 8 years of age. Results: At age15, slow readers made more errors during text reading and word reading, showed similar hyperactivity but more inattention symptoms, and similar non-verbal abilities but weaker verbal abilities than the other readers. At age 8, they had more difficulties in reading tasks, similar hyperactivity but more inattention symptoms, and more difficulties in rapid naming and phonological analysis but similar performances in phonological memory and temporal processing (p < .05). Conclusion(s): This suggested that adolescents who read more slowly already presented more inattention symptoms and difficulties in reading, phonological analysis, and rapid naming when they were children, underlining the need to intervene in order to prevent later reading difficulties.