Joan Hillsman never knew her father, who was killed in World War II when she was just a toddler.

But she knows his music.

Her father, Pvt. Bill Rucker, loved to sing "hip-slapping, old-style" gospel music, she said. He was 22 years old when he died.

Her grandmother kept telling her to learn her father's music as a way to get to know who he was. "She kept telling me, 'You've got to carry on this music. You have to learn to sing like your father.' "

Her mother and grandmother bought her a toy piano. Soon, she was pounding away on a real piano. Then she was playing piano for Sunday school and the church choir.

But she kept playing the "church music" straight, just as it was written on the sheet music.

"So they told me to add something to it, to add movement so we could swing and hear the beat," she said. "And as I played, I used to think of my father watching me."

Hillsman mastered her father's music, and went on to become an expert on teaching gospel music.

At 17, she left her home town, Anderson, S.C., to attend Howard University, where she received a master's degree in music education. She received a doctorate in music from Union Institute in Cincinnati, writing her dissertation on gospel music.

Today, at 47, she's the assistant director of music for D.C. public schools. She recently wrote a book, "Gospel Music, an American Art Form," which traces gospel's African roots and provides lesson plans for music teachers.

She said black children need to understand gospel to understand their heritage.

"If we don't teach it to the younger generation, we'll lose the oral tradition," she said.

There's a catch, of course. Because of the Supreme Court decision banning prayer in public schools, Hillsman said teachers must be careful when teaching gospel music in classrooms, making sure to avoid discussing the religious concepts behind the songs.

Instead, the focus must be on learning to harmonize and improvise, key components of gospel music, and secondarily on the history of the music.

But at Mount Joy Baptist Church on Fourth Street SE, where Hillsman directs a gospel choir, she instructs the choir to "sing it like you mean it."

"Let me hear you moan!" she shouted as she pounded the piano with one hand and guided the choir with the other. The 33 members of the chorus fixed their eyes on her, moaning and groaning to her every gesture. Hillsman spent 10 minutes teaching them how to sing the words "Oh Lord" in the song "Mary Had a Baby."

This wasn't just an ordinary birth," she told them, "so we aren't blase' when we sing about it."

Gospel began to develop after the decline of slavery, she said. It replaced the mournful plantation songs with "happy, jubilant" music, fusing elements of blues, jazz and the old spirituals. During the civil rights movement, gospel melodies were converted into freedom songs, she said. "We Shall Overcome" had been sung in black churches for generations, but back then it was called "I'll Be Alright."

Hillsman writes her own gospel songs, hosts a weekly gospel show on WYCB-AM (1340) and has traveled around the world spreading her enthusiasm and knowledge of gospel music.

When performing, she still thinks about her father. "Even as an adult," she said, "I sometimes think, 'I wish Bill could see me now.' "