Conan hadn't figured out yet that being an elementary school detective was something that needed to be defined and explained.

"I'm an amateur detective," he says with some annoyance. "At home there are a lot of teenage detectives who assist the police with difficult cases. Private individuals also ask them to look into things. I just got started on it younger than most. I mostly assist other detectives."

By solving the cases for them and then letting them think it was their own idea all along.