Whyever would they need to?
As he has always been, the President is free to address the issue of education in any forum he might choose -- Congress, a televised address to the nation, a press conference, an interview with the press, etc.
Moreover, President's have always been -- and will continue to be -- free to address students specifically within the context of such speeches.
Indeed, Presidents have always been -- and will continue to be -- free to accept invitations and make commencement addresses, the primary audience of which is...students.
Thre is no good purpose served by an uninvited President focussing an "education" address to grade school children in a "national classroom". The only identifiable purpose is indoctrination.
No other President would've even thought to produce such an act.
When Ronald Reagan addressed America's students following the Challenger crash, was that a bad thing? When George H.W. Bush had a nationwide student address on drugs, was that a bad thing? Neither was necessary, both were good ideas. But now? Any future Republican president who might want to do it will run into the same boycotts and charges of indoctrination that Obama is getting.