August 17, 1987 12:00 PM

Okay, so it’s more of a lark than summer school. But dancing in Madonna‘s Who’s That Girl tour is a rigorous education in its own way. Just ask Chris Finch, the nimble 13-year-old who prances and struts through a good portion of the Material Girl’s stage numbers this summer.

For one thing, Finch says Madonna taught him how to work. “We ran five miles together when we were in Montreal, and sometimes we run up steps,” Chris says. “That’s hard.” He also learned about not taking showbiz too seriously. “At one point during the song Live To Tell, when her back is to the audience and I’m going offstage, she makes funny faces at me and I crack up,” he says. “She teases me that she’ll trip me if I mess up.” And last month, at a concert in his hometown Anaheim, Calif., Finch learned about getting too much of a good thing. After belting out the final phrases of Like a Virgin, Madonna planted an extra-special kiss on her sidekick’s authentically virginal lips. “She knew all my friends were going to be there so she kissed me longer than usual,” Finch says, blushing. “I lost my place and couldn’t remember the next steps in the number.”

Stumbles like that are a rarity for Finch. “I showed him some soulful moves at his audition and he picked them up right away,” remembers Shabba-Doo, the tour’s choreographer. “That’s why I knew he was the one.” So expert was Finch’s tryout number last spring that Shabba-Doo and Mrs. Penn herself couldn’t resist dancing in a circle with him. “I remember thinking that even if I didn’t get picked for the show, at least I got to dance with Madonna,” Chris says.

Madonna is obviously pleased with her chosen one. “He’s the ideal man,” she says, only half-kidding. “He does everything I ask him to do and never complains.” As Madonna vamps her way through her repertoire, hands sliding up and down her thighs, Chris twirls blithely beside her. His costume changes are almost as frequent as hers: One minute he’s a mini-David Byrne wearing an oversize suit, the next a flamenco dancer in sequined jacket or a Fred Astaire in tails.

Though the show doesn’t always project the purity one might expect from such a May/December partnership, it did win parental approval. “I guess we’re pretty open-minded,” says Chris’s father, Larry, 45. “I get tears in my eyes when I see him dance with Madonna. I think, there he is, onstage with one of the most popular performers in the world.”

Finch’s parents cannot, however, be accused of pushing him into the gig. Three years ago Chris had to plead with his father, a former child actor who now owns his own construction company, for permission to take acting classes. When his parents gave their okay, Chris found that local acting workshops were full, so he enrolled in jazz dancing classes instead. Soon he had an agent, was studying ballet and modern dance, and made a guest appearance with the New York City Ballet. Now he has shown his stuff in Madonna‘s Who’s That Girl video. (Though the two are often confused, a different boy, Briton Felix Howard, 14, dances in her Open Your Heart video.)

The tour has brought Finch some unusual perks, such as meeting Don Johnson, Bianca Jagger and Pee-wee Herman backstage. “Jack Nicholson told me I did real good and that I’d be a star someday,” he says. What’s more, Madonna has made a point of getting chummy with her partner, inviting him home for dinner and introducing him to her unpredictable husband. “Sean’s a great guy,” says Chris. “We played tennis in Miami, and when we were in New York we went lingerie shopping for Madonna. We got her underwear with, like, leopard patterns.”

But this summer comes with one downer that Chris’s sister and two brothers won’t have to face. “Where are your books?” Madonna asked at the first rehearsal. Then she insisted along with his parents that a tutor coach him during the tour, in preparation for his September return to the ninth grade at Loara High School. By that time, he will be a little richer (“enough to pay for college twice,” says Larry), a little taller (two inches since June) and maybe, just maybe, a little harder to handle. “We’ll try to keep things the same in our lives,” says Larry. “He’ll still have to take out the trash.” Says Chris, breaking into a grin: “No way.”