A high school musical is already something of a circus, with its carnival atmosphere, heroes and clowns, infectious music and audience of all ages.

So why not harness all that and go right to the thing itself, as with the musical "Barnum"? That was the animated spirit behind last weekend's Keystone Oaks High School production of the 1980 musical comedy by Cy Coleman, Michael Stewart and Mark Bramble.

"Barnum" isn't entirely a circus musical. It concentrates more on P.T. Barnum's early career of razzle-dazzle, focusing less on celebration of sawdust and tinsel than ironic exploration of entrepreneurial genius, in the satiric style of other musicals of its decade, like "Pippin."

But the circus motif runs all through it, and there's plenty of opportunity for the cast to portray clowns, contortionists, jugglers, magicians, aerial acts and other midway performers, not to mention such Barnum headliners as General Tom Thumb and Jenny Lind, the Swedish Nightingale. And under the expansive direction of Richard Fosbrink, the spirit of the carnival midway spilled over the footlights, making Keystone Oak's "Barnum" more than just a musical, but an encompassing experience of circus-themed fun.

It started in the lobby, an hour before curtain, with a variety of juggling and clown acts. I was especially taken with the Siamese Twins played by sunny real-life twins Jackie and Melissa McCarthy, who were able to handle banter as capably as they juggled. The lobby also held an expansive mart of balloons, flowers and carny food (hot dogs! sweet stuff!), ushers in candy-striped vests and a huge raffle orchestrated by Mary Windstein featuring 40-some large prize baskets of every variety.

With that cheery midway for context, the show had a head start before the lights even dimmed -- as what high school show doesn't, come to think of it, since audience and cast already create a community of shared interest.

I chose Keystone Oaks as one of the schools to write about during this year's high school musical season because the only year I'd ever been to its musical was 1992, when the subsequent newspaper strike blanked out the review I wrote, and in a lifetime of musical comedies, I'd only seen "Barnum" once -- at Point Park in 1999.

The result? I enjoyed the musical itself, but I really loved what Keystone Oaks and Mr. Fosbrink and company did with it.

"Barnum" had a more than two-year initial run on Broadway, where it starred Jim Dale, with Glenn Close as his dour wife. It won Mr. Dale the Tony Award, and in London it won the equivalent honor for a pre-"Phantom" Michael Crawford. But it just isn't revived that often -- Pittsburgh CLO has never done it, not even for James Brennan.

It did launch a couple of lasting songs, though, in "Come Follow the Band" and "Join the Circus." There are also some clever patter-songs, in the style of Gilbert and Sullivan. It packs a lot into a little more than two hours.

It paints Barnum mainly as a magician of appearances, the master of hucksterism, hocus-pocus, poppycock and spin. Along the way he turned museums from staid collections of the past into aggressive entertainers.

The musical has a taste for probing metaphor, such as the actual tightrope Barnum walks, leading from his wife to his affair with songstress Lind. But as it tells its up-and-down life story of the obsessively extroverted showman, "Barnum" has the smarts to harvest the circus' flash and color, its pungent smells and swagger.

At Keystone Oaks, an all-purpose, one-ring circus set complete with two tent poles doubled as the normal world of the mid-19th century. The costumes by Michael Perkins and Ginny Pfatteicher painted a rainbow of color, and although this isn't a dance show per se, Scott Taylor's choreography provided bursts of lively movement. Mary Kelly Rayel and Matthew Duncan were the indispensable circus trainers.

P.T. himself is a giant role, and Justin Tunney filled it with enough effusive brass and pizzazz to compensate for a modest singing voice. The stronger vocals came from Casey Daugherty (Barnum's wife, Charity), Robyn Cheeseman (Lind) and Rachel Geraci, who scored with Tom Thumb's big number.

There were too many other contributors to list them all, but the standouts included Melanie Gumina's blues singer, Logan Shipp's stentorian ringmaster and the dancing gymnastics of Lauryn Fawcett.

Keystone Oaks is a participant in Pittsburgh CLO's 19th Gene Kelly Awards for Excellence in High School Musicals, which will hold its big awards gala May 23 at the Benedum. That may not be the greatest show on earth, but it's close to the best in Pittsburgh.