WASHINGTON -- The White House on Friday dismissed as "silly" the controversy over President Obama's plan to address the country's schoolchildren to mark the start of the school year.

"I think we've reached a little bit of the silly season when the president of the United States can't tell kids in school to study hard and stay in school," Press Secretary Robert Gibbs said. "I think both political parties agree that the dropout rate is something that threatens our long-term economic success."

The White House said earlier this week that the president's address Tuesday is intended to be an inspirational, pro-education message to all students at the beginning of the school year. But critics objected to the language of one of the lesson plans, for students in pre-kindergarten through grade 6, that suggested that students "write letters to themselves about what they can do to help the president." Another assignment for students after hearing the speech was to discuss what "the president wants us to do."

The suggestion about writing letters has since been changed to: "Write letters to themselves about how they can achieve their short-term and long-term education goals. These would be collected and redistributed at an appropriate later date by the teacher to make students accountable to their goals."

But some schools across the country are wrestling with the question of how -- or whether -- to present the president's speech. And some parents, outraged by what they fear will be an indoctrination speech, have said they'll go as far as to keep their children home from school rather than allow them to watch.

White House spokesman Tommy Vietor said the changes to the language are intended to make the lesson plans clearer. He added that the president's speech will not be a policy speech, but is intended to encourage kids to work hard and commit to school.

Randi Weingarten, president of the American Federation of Teachers, on Friday defended Obama's plan to address students.

"The bottom line is we need the president of the United States of America to use his bully pulpit to talk to kids about the importance of education and to help inspire kids," she said on radio station WOR in New York.

Gibbs said former Republican presidents Ronald Reagan and George H.W. Bush delivered similar speeches to students. He said Obama's speech will not be partisan but rather a chance for children to get "a little encouragement as they start the school year."

The White House spokesman said he couldn't speak to the motivations of some school districts.

"Look, there are some school districts that won't let you read 'Huckleberry Finn,' " Gibbs said.

He said the administration understands that some districts have logistical concerns with the timing of Obama's noon ET speech.

The White House plans to release the text of the speech online Monday so parents can read it. Obama will deliver the speech at Wakefield High School in Arlington, Va.

The Associated Press contributed to this report.