This study seeks to quantitatively describe the association between ADHD, ADHD subtypes and processing speed using meta-analytic procedures. Analyses are guided by the following research questions: What is the magnitude of the mean effect size for processing speed in children with ADHD compared to children without ADHD? What is the magnitude of the mean effect sizes for processing speed in children with ADHD across subtypes compared to each other and those without ADHD? Relevant articles were identified by keyword searches of the EndNote X4 program database. This process identified 424 contemporary research articles, which were subjected to inclusion criteria. Meta-analyses investigated the distribution of standardized mean difference effect size statistics (Hedges's g). Results indicated significant effect sizes for processing speed in the moderate range for youth and adolescents with ADHD compared to youth and adolescents without ADHD. Findings did not support significant differences in mean effect sizes between ADHD subtypes.