Factcheck.org today does an excellent job as usual. Two exerpts I found very interesting:
We’ve also gotten a number of queries about whether any previous president has addressed the nation’s schoolchildren. President George H.W. Bush did so in 1991, when his address to an eighth-grade class at Alice Deal Junior High in Washington, D.C., was broadcast nationwide. The administration sent letters to all public schools urging them to watch the speech, which ended with Bush encouraging students to "write me a letter about ways you can help us achieve our goals."
...
President Ronald Reagan also gave a televised address to schoolchildren in November 1988. His speech had more political content than Bush’s or Obama’s, touching on taxes and the spread of democracy. We found no reports of objections to that speech.
This shows how hypocritical Republicans are.
http://factcheck.org/2009/09/obamas-speech-to-schools/