What instructional approach is likely to expand the syntactic development of a student using AAC?

Demonstrating symbol combinations is crucial for expanding the syntactic development of a student using Augmentative and Alternative Communication (AAC). This approach directly encourages students to understand how to combine different symbols or words to create more complex messages. By modeling these combinations, the student can see examples of how syntax functions in practice, which helps them grasp sentence structure and formulating more elaborate expressions. This method aligns with language modeling strategies that are effective in fostering both comprehension and production of language in AAC users.

The other options, while beneficial in various contexts, do not target syntactic development as directly. Visual aids can support comprehension and provide context, high-performance rewards may motivate participation but do not specifically enhance syntax, and direct instruction on vocabulary is important for language development, yet it does not inherently teach how to combine those words into sentences. Thus, demonstrating symbol combinations stands out as the most effective approach for advancing the use of syntax in AAC communication.