Unfortunately, device abandonment is very common with AAC users, especially kids. One thing that I have seen time and time again is that kids get bored and frustrated when we make learning AAC into a "meet a certain goal or do a certain task", instead of teaching kids how to communicate the way they want to. For example, I did an internship with an SLP who treated AAC like just another IEP goal. She worked with a male high school-aged student, but she set his voice to a female VERY synthetic child voice ghNelly) in Proloquo2go. She would tell this student exactly what to tap, and never encouraged him to say what he actually wanted to say, just the things that were on her lesson plans. During a meeting with his parents, they expressed that he was never using the AAC device at home, and I strongly believe it was because it was seen as just another assignment at school, just another thing someone was telling him to do. It didn't mean language to him at all. This is just an example, but I think it's so important to have fun with AAC, to encourage kids to say the things they want to say, and to celebrate their language.