In return, Lambert, 27, offered the crowd at Mt. Carmel High School two songs and a few words of appreciation.
"This is so weird," he said, thanking the crowd from a makeshift stage on the packed stadium's field. He advised students to "believe in yourself" no matter what others may say.
His entrance — in a cherry-red convertible — was heralded by the screams of cheerleaders. The marching band played as Lambert slowly cruised the stadium track, drawing shouts from the bleachers.
Lambert's renditions of Michael Jackson's "Black or White" and "Mad World" won applause despite a tinny sound system.
His "American Idol" competitors, Danny Gokey of Milwaukee and Kris Allen of Conway, Ark., were also feted by their towns Friday, with Fox taping the events to air next week on "Idol."
The winner of Fox TV's singing contest will be announced on the May 20 "American Idol" finale.
In San Diego, a woman wearing a sports bra but sans blouse rushed the stage to get closer to Lambert and was quickly hustled off. When Mayor Jerry Sanders stepped up to declare Friday "Adam Lambert Day" in San Diego, he jokingly vowed to keep his shirt on.
The stadium was draped with banners reading, "Mt. Carmel (Hearts) Adam!" and, "You're Our American Idol." A poster toted by a fan proclaimed, "Adam, You're a Rock God" — echoing show judge Kara DioGuardi's assessment of Lambert, who has performed in musical theater.
He's been a consistent favorite with the "Idol" judges, even the tough-minded Simon Cowell.
Lambert was a standout in high school, too, said Bryan Clark, 26, of San Diego who graduated in the class of 2000 with him and attended the celebration Friday.
"He was definitely good," said Clark, who recalled seeing Lambert perform at pep rallies and other school events. "I'm proud of the guy. It's always good to see people making their dreams happen."
Geri Johnson, along with granddaughter Olivia Mercado and her young friends, had been on Lambert's trail since 5 a.m. Friday, when he visited local radio and TV stations.
"It was pretty rowdy," Johnson, of nearby El Cajon, said of the early morning crowd. So why did they make the effort?
"He's really cute," said 12-year-old Mercado. Friend Quiana McMorris, 15, who brought along a stuffed animal as a gift for Lambert, offered her view: "He's a really good singer."
Robin Andersen came to Mt. Carmel High from nearby Carlsbad with her 13-year-old daughter, d'Lainey Forrester, because "you always have to support hometown people. Plus, I think he's going to win."
Asked if she thought Lambert — who favors black leather and matching nail polish — might prove too bold for the American audience, Andersen had a quick response: "My 88-year-old mother thinks he should win. And she's as conservative as they come."
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