"Just one request," says Ann Chapman to her interviewer, "Please don't do a sob story."

The request is easily granted -- for hers is an upbeat story of a popular tap-dance teacher with a devoted student following. Each year she teaches scores of children and adults from Montgomery and Prince George's counties and the District to tap their way across the stage in musical productions that she writes and directs.

There's nothing sad about that. Indeed, it's rather remarkable when you discover that Ann Chapman is blind.

The students are always forgetting that, anyway. At the dress rehearsal for a production, a little girl dashed up to "show" the teacher her costume. And when Chapman asked if cast members were in place for the next number, they nodded, prompting her to quip:

"You know, you have to shake your head real loud when you're talking to me."

There were more than 50 toe-tapping, finger-snapping members of this particular cast, ranging in age from 6 to 60, and Chapman, herself 70, has the voices and names straight. She has shown them all what to do and she can hear when it isn't done right.

"Well, I can't tell when it's the wrong foot, but I take comments from the students. It makes them be observant and helpful, though I don't want them to pick people to pieces."

She stands at the edge of the stage in the District's Chevy Chase Community Center, where her classes are held and gives stage directions. But how can she do choreography?

"I have mental pictures from the earlier past when I could see," Chapman explains. But in her youth in Blackfoot, Idaho, her sight was deteriorating at a steady rate. "By high school, I couldn't really read print. I had mobility, though, and dancing was a good profession."

After 10 years of teaching it there, Chapman came to Arlington County where she taught from 1940 to 1960 without anyone officially noticing her blindness.

It wasn't "deception," she hastens to note. "If anybody had asked me, 'How come you can't see that?' I wouldn't have lied.

But was there a fear of prejudice in hiring?That's still a problem among the handicapped, she says. In her case, coming to grips meant "learning to accept yourself first and then other people accept you. It's saying, 'I'm blind and need help; help me and I'll do my part.'"

After Arlington, Chapman took up Braille and worked with blind children at the Columbia Lighthouse for the Blind here.

During and after her formal-but-not-final retirement from the Lighthouse, she returned to tap-dance instruction, with blind as well as sighted children at the Chevy Chase Center. She brought along one of blind students from the Lighthouse, Linda Kipps, who not only dances, but plays the piano and sings beautifully.

"I've known Linda since she was 5. She worked herself into a job at the center, which helped her with tuition at American University, as a major in voice.

"I guess she's more or less my protege, and you know, it's nice for me to have a young friend like that."

During one recital break, Linda Kipps, who is in her late 20s, did an impromptu piano and vocal rendition of "I Could Have Danced All Night." The cast could have, too -- or so it seemed in the clackety-clacking hall as final touches were made for the big night.

After the main performance at the center for families and friends, the troupe usually takes the show on the road, for appearances at places such as the Wisconsin Avenue Nursing Home and the Roosevelt Hotel for Senior Citizens.

During summers, Chapman works just as feverishly with downtown neighborhood children at the Lighthouse day camp.

Among her students everywhere, an excited concentration seems to obliterate any anxiety or distraction that might develop in this kind of encounter.

To them, Ann Chapman is extraordinary -- but not because she is blind.