The current research comprised two studies to investigate the emergence of derived relational responding in children with Global Developmental Delay (GDD). In Study 1, four children diagnosed with Autism Spectrum Disorder (ASD) and one child with Down's syndrome, were exposed to verbal assessments (the Verbal Behaviour Milestones Assessment and Placement Program, VB-MAPP; the Kaufman Brief Intelligence Test, K-BIT; and the Peabody Picture Vocabulary Test, PPVT) following which they were exposed to relational responding testing and training in the following sequence: co-ordination, distinction, comparison, opposition and hierarchy. All children demonstrated different levels of verbal and relational responding competencies however overall an intervention based on RFT was found to be successful in establishing relational responding in accordance with the targeted frames. In Study 2, four participants with ASD were exposed to a training sequence identical to that used in Study 1 however the location of comparison and opposition were alternated. Results found that participants in Study 2 demonstrated significantly better performances in the emergence of comparison relations than those in Study 1 suggesting that the manipulated sequence may have had an effect. Results also support the previously suggested developmental sequence of the emergence of derived relational responding with evidence of some relational frames emerging before others found. Furthermore results provide evidence of a relationship between relational responding and verbal ability.