I got a message from the parent of a student who goes to a school I did a talk at during book week who said "I inspired her son to come home and write a story" and jesus christ has that made my day/week/year. I don't get them that often, but every time I get a message from a parent saying something like that it just means so much knowing there is a kid out there writing his own story now.
I heard some time back that the news media have a rule of thumb - for every person that rings them up about an issue, there are 10 more that want to but don't. For every person that writes a letter, there are a hundred more that want to but don't. So I assume that a message would be somewhere between the two? So there's probably a lot more people out there that appreciate your work.
I sure hope so. Even if I don't know about it, as long as it's encouraging reading and writing in kids, that's all the matters. Getting these messages certainly makes my day though.