Every object can act as an particle or wave. The higher the particle (mass) the lower the waves get. Same way around.

Probably light has the perfect balance between particle and wave so it can be shown as both. (I’m not a scientist, just looked it up real quick.)

….. It depends on how you experiment with light. You can experiment with an solution that says light acts as particle or get experiments that say light acts a wave. Don’t really know how to explain in detail in the English language as a non-native.

If you can break down the explanation of the link below maybe you can help your student find an answer.

https://theconversation.com/curious-kids-is-light-a-wave-or-a-particle-162514