It all began with thousands of young hopefuls. Optimism soared. Talent sometimes didn't.

Now "American Idol" concludes tonight and Wednesday (7 p.m., Ch. 13) with two people. The difference might come down to choosing the right songs.

Susan Slamer and Debra Byrd know that. As the "Idol" music director and vocal coach, respectively, they've seen extremes.

A high: Last year, Fantasia Barrino chose "Summertime" — a song she'd never heard of written 50 years before she was born.

"She said, 'I chose it because I feel it . . . and I know exactly how I'm going to do it. I'm going to sit on the floor, barefoot,' " Byrd recalls.

Barrino promptly drew raves and won.

A low: This year, singers could choose any song from the year of their births. Nadia Turner chose "When I Dream," an obscure 1977 song.

"She said, 'I'm going to choose a Crystal Gayle song,' " Byrd said. "I said, 'Okaaaay.' I even said, 'Is this your final answer?' "

It was. Judges grumbled and viewers failed to vote to keep her on.

Such extremes start anew each week. New categories are announced; the decisions begin.

Some categories draw groans. But while others in the first season were groaning about big-band week, Kelly Clarkson instantly announced she was doing a song from the Bette Midler movie "For the Boys." While others in the current season floundered during Broadway week, Constantine Maroulis was at ease — he's a musical-theater veteran.

At times, definitions are disputed. During dance-song week, producer Nigel Lythgoe argued that Bo Bice's choice ("Vehicle," by The Ides of March) didn't fit the category.

"I told him, 'Excuse me, but in my neighborhood we danced our butts off to that song,' " Byrd recalls.

Some weeks are naturals for the young singers. Barry Manilow's songs, with their direct melodies, went smoothly. Elton John's complex ones created a rough week.

One person, however, conquered a John song. "Jennifer Hudson had sung 'Circle of Life' hundreds of times," Byrd says. "She came in with an arrangement and a tape recording."

That repetition helps. Bice does songs he's been doing in rock clubs for years, while others sometimes struggle to learn them in a week.

Each singer faces different challenges, Byrd says. "For Carrie (Underwood), it's personality. For Anthony (Fedorov), it was focus."

Underwood is a country singer, content to stand and emote. But she's learning. When she growled "I'm evil" and kicked over a microphone stand, the crowd was delighted.

Vonzell Solomon has needed no nudging. "Vonzell just oozes personality," Byrd says.

As Underwood stretches for that same kind of energy, she faces complications. "Piece of My Heart" was a blistering Janis Joplin rock song in 1968, then a Faith Hill country song in 1994. Underwood tackled it.

"She listened to the Faith Hill version," Byrd says. "That's the one she aligned with."

Judges didn't. Instead of crediting her for a good Faith effort, they criticized her for doing bad Joplin. The road to idoldom is full of difficult detours.