2.1. Participants

Two groups of children participated in this study and were assessed at three times. The first evaluation was at the time of diagnostics (Time 1), followed by an evaluation after the first phase of the intervention, consisting of 12 treatment sessions (Time 2; see Tilanus et al., 2016). The final evaluation took place after the second phase of the intervention, which consisted of 36 additional treatment sessions (i.e., after a total of 48 treatment sessions; Time 3). The first group were Dutch second graders with diagnosed developmental dyslexia (N = 122). They were referred to a clinic by their parents following advice from the school. This group started intervention throughout second grade. Children's waiting time, the number of days between initial assessment and treatment, varied and was therefore taken into account (M = 80.44 days, SD = 34.03 days). The group consisted of 75 boys and 47 girls with an age ranged from 7 to 8 years at pretest and 83 children repeated a class. All children met the formal criteria of dyslexia in accordance with the definition of the Dutch Dyslexia Foundation (Stichting Dyslexie Nederland, 2008) and the American Psychiatric Association (2013). According to this definition, dyslexia is an impairment characterized by persistent problems in learning to read and/or write words or in the automatization of reading and writing. The level of reading and/or writing has to be significantly lower than what can be expected based on the educational level and age of the individual.

The control group consisted of 108 typical readers (56 boys, 52 girls) in second grade with an age between 6 to 8 years old at pretest. Three children had repeated a class. This group was selected randomly out of the lists of schools of the children with dyslexia to function as a control group.