Children with limited speech and motor function, frequently subsequent to neurodevelopmental conditions, often require augmentative and alternative communication (AAC). Assessment practices to inform effective AAC interventions for these children can be challenging because of the considerable heterogeneity and range of factors that require consideration. An improved understanding of current assessment practices is imperative to optimize the provision of AAC. We conducted a scoping review to identify the assessment practices used with children with limited speech and motor function subsequent to neurodevelopmental conditions (birth to 18 years) within the Participation Model of AAC. In total, 171 assessment practices were identified. Almost all were related to access supports and barriers, of which the majority focused on children’s capabilities. Relatively few methods were identified to support the assessment of children’s participation patterns and communication needs or opportunity supports and barriers. Twenty-three percent of identified formal assessment practices required modifications to established procedures, and 10% could not be completed by all child participants. Identified assessment practices focused primarily on children and their abilities, whereas very few focused on external factors (e.g., environmental and opportunity supports and barriers). Additionally, identified assessment practices may inaccurately measure the abilities of children with limited speech and motor function, as the procedures often required modification.