"You are aware of how abnormal that is, right? Helping out the police but not going to school. If it was just Sherlock you were living with it wouldn't matter because those kinds of thoughts don't really occur to him. He doesn't look at you and think that you should be getting an education."

John on the other hand - people would wonder why the good doctor wasn't looking after this kid that suddenly landed in his lap. At this point Conan has already put together that the need for a list of places he was going to be that day happened on the same day that the doctor arrived.