I think it may depend on what your child is like to some extent. DD is very outgoing and "showy," (she is the kid who raises her hand every time) so we haven't felt a need to talk to teachers ahead of time. IOW, she is hard to miss. However, I know some kids are quiet or shy or do not display what they know. I would still give it a couple of weeks' time before scheduling a conference, though. I think teachers like to see the kid for themselves first.