Both Williams syndrome (WS) and Autism Spectrum Disorder (ASD) have been characterized as preferentially processing local information, whereas in Down syndrome (DS) the reported tendency is to process stimuli globally. We designed a cross‐syndrome, cross‐task comparison to reveal similarities and differences in local/global processing in these disorders. Our in‐depth study compared local/global processing across modalities (auditory‐verbal/visuo‐spatial) and levels of processing (high/low) in the three syndromes. Despite claims in the literature, participants with ASD or WS failed to show a consistent local processing bias, while those with DS failed to show a reliable global processing bias. Depending on the nature of the stimuli and the task, both local and global processing biases were evident in all three neurodevelopmental disorders. These findings indicate that individuals with neurodevelopmental disorders cannot simply be characterized as local or global processors. This cross‐syndrome, cross‐task, cross‐modality comparison demonstrates that, in contrast to the traditional view, individuals with a neurodevelopmental disorder cannot be characterised as having a specific local or global processing style. Here we show that—contrary to claims in the literature—participants with Autism Spectrum Disorder or Williams syndrome failed to show a consistent local processing bias, while those with Down syndrome failed to show a reliable global processing bias.