"At the end of the day, if the president motivates one C-student to become a B-student or one student who is thinking about dropping out to stay in school and take their education seriously, it's all worth it," Duncan told CBS News chief Washington correspondent and anchor Bob Schieffer on "Face the Nation" Sunday.
The secretary even added some criticism of his own.
"It's amazing to me the last time the president spoke to the nation's children was in 1991," Duncan told Schieffer. "The real question I have is, why has it been 18 years since a president has addressed our nation's youth?"
Mr. Obama is expected to deliver his speech live on the public affairs channel C-SPAN and via the White House's Web site at noon Eastern time Tuesday, which will be the first day of school for many students across the country.
Schieffer asked Duncan what he thought about some reports that parents who oppose the president wouldn't send their children to school that day because of the speech.
"That's just silly," Duncan told Schieffer. "They can go to school and not watch. It's just going to be an 18-minute speech. That doesn't make any sense. … Schools can do this. They cannot do it. They can watch it during the school day. Children can watch it at home with their families. They can watch it a month from now. They can never watch it. It's purely voluntary."
More coverage of Mr. Obama's message to students from CBSNews.com
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W.H.: School Speech Criticism Reflects "Silly Season"
Schieffer on Obama's School Speech
"Washington Unplugged:" Debate Over Obama Address
Conservatives Revolt Over Obama Speech to Students
Duncan added that the text of the speech will be made available to the public through the White House's Web site on Labor Day for anyone to read in advance.
But the secretary said his department doesn't pay any attention to the recent attacks.
"We have major problems, major challenges in this country," Duncan told Schieffer. "We have more homeless students than we've ever had and teachers and social workers and counselors working so hard to keep them in school. … We have a 30-percent drop-out rate. Thirty percent don't graduate from high school. That's 1.2 million students every single year … This is about global competitiveness. I don't spend any time on the silly stuff. I try to focus on improving what's going on for our nation's children."