As they neared Central, word spread via social media that Corbett would be a no-show.
He had planned the visit to honor students at Central, J.R. Masterman High School, and George Washington Carver High School for their high test scores.
Marisa Block, 25, a Central graduate who was one of the protesters assembled in front of the high school, called the governor's decision "shameful."
"He's not willing to face the protesters who are out here," said Block.
At a news conference in his office in the Bellevue, Corbett told reporters, "I don't run from anything. I face things head on."
Of his decision, he said, "I was not going to engage in any theatrics the adults had planned."
Corbett administration insiders, who asked not to be identified because they were not authorized to speak publicly, said the governor became concerned that the planned protests could spill inside, risking student safety.
There was also concern that his presence would become a distraction, turning an event meant to highlight student success into political theater, they said.
Political opponents wasted no time in criticizing.
"Tom Corbett cannot lead Pennsylvania if he is too afraid to look students, parents, and educators in the eye while explaining his cuts and failed education policies," said Tom Wolf, a Democratic candidate for governor.
U.S. Rep. Allyson Y. Schwartz, also a Democratic candidate, whose two sons are Central graduates, said, "After denying public schools the resources they need to educate our children, it is an affront . . . that Gov. Corbett has canceled what would have been his first visit to a Philadelphia school."
The criticism came one day after Corbett pledged to propose hundreds of millions of dollars in new education funding.
To the assembled protesters, Galeet Cohen, a Central alumna and a biology teacher at the school, read an open letter to Corbett from the staff that expressed "discomfort" with his visit.
"We are proud of and celebrate our students' achievements, yet we recognize that they have accomplished this in spite of, rather than because of, your budget cuts and educational policies," the letter said.
Inquirer staff writer Kristen A. Graham contributed to this article.