"We know what the key is, put their kids and their parents and their teachers first and put the teachers union behind," he said.
Earlier Sunday, Obama for America held a press conference talking about Romney's education record.
"There couldn't be a clearer choice between the president's commitment to education, and the rhetoric of the Romney-Ryan ticket, which would slash funding for education at a time when we need to be investing in our students and teachers," said Sen. Michael Bennet, a Democrat and former Denver schools chief.
Garcia said Sunday the campaign was targeting women and Hispanics in the coming 45 days until the election. The Romney campaign estimates there are 98,000 unemployed women in Colorado.
"I think people are really disappointed in the promises" President Barack Obama made four years ago, Garcia said. "The reality has sunk in."
Joyce Boehland, a 75-year-old from Arvada, attended her first political rally Sunday and said she liked "feeling the essence" of the candidate instead of just seeing him on TV.
"I feel better now," she said, putting on her shoes after standing for a long time on the football field. "I heard real steps tonight."
GOP state chair Ryan Call told the crowd Sunday that Colorado had an "outsized" role in this election. President Barack Obama has visited Colorado nine times so far this year.
Romney's vice presidential candidate Paul Ryan will come to Colorado Wednesday for a town hall in Fort Collins and a rally in Colorado Springs.