The reality, which opened the Rep’s 35th season July 23, is pure, infectious joy, directed by Sam Woodhouse, whose heart is always in the right place. This time the heart shows right before one’s eyes. It’s touching. It’s impeccably done. It’s infectious.

The invisible 25-piece orchestra, composed entirely of student musicians, sounds like pros under Tamara Paige’s baton (Bill Doyle is musical director), playing Harold Wheeler’s orchestrations and Marc Shaiman’s arrangements. The more visible students sing and dance beautifully, backing up the leads and, in the case of diminutive SDSCPA powerhouse Victoria Matthews (Little Inez), very nearly stealing the show.

Set in Philadelphia in 1962, the musical’s Tony Award-winning book (Mark O’Donnell and Thomas Meehan) is based on the 1988 New Line Cinema film written and directed by John Waters. It concerns Tracy Turnblad (Bethany Slomka, a former SDSCPA student, now a college sophomore), a chunky teen with big hair and a penchant for dance and song. Tracy is an avid viewer of the “Corny Collins Show,” one of those early TV dance shows with teens from the local schools. Tracy auditions, and though producer Velma Von Tussle (Leigh Scarritt) opposes letting her on the show, Collins (Victor Hernandez) and Seaweed J. Stubbs (Tony Melson) make certain she stays. Tracy falls in love with the current Miss Hairspray’s (Megan Martin) beau, teen idol Link Larkin (Efren Ramirez) and works relentlessly to racially integrate the “Corny Collins Show.” Velma and the show’s sponsor, Harriman F. Spritzer (Tim Irving), oppose both “negroes” and “race music,” and the African American kids are allowed to dance on the show only once a week, and then only in the background.

Because the school principal (Irving) banned her big hair, Tracy is frequently in detention. There she runs into Seaweed again and through him meets his mother, Motormouth Maybelle (Pam Trotter), her daughter Little Inez, and the talented kids that hang out and dance in Maybelle’s record store. Eventually they forcibly integrate the dance show and Tracy gets the guy. Her best friend, Penny (Stacy Hardke), falls in love with Seaweed.

Other major characters in the musical are Tracy’s parents, Edna (Peter Van Norden) and Wilbur (Steve Gunderson) Turnblad, who love Tracy and, in this production so humanely and humorously played, adore each other. Van Norden and Gunderson, whose duet, “(You’re) Timeless to Me,” brings down the house, sincerely and affectingly play the roles originated on Broadway by Harvey Fierstein and Dick Latessa, both of whom copped Tony Awards in 2002, as did director Jack O’Brien, creators O’Donnell, Meehan, Shaiman and Scott Wittman for Best Book and Best Musical, and Marissa Jaret Winokur for Best Actress.

The Rep/SDSCPA production is enhanced by Javier Velasco’s choreography, scenic and lighting design by Trevor Norton, and costume design by Mary Larson and Kate Stallons. Tom Jones’ sound design is not always balanced between soloist and chorus, but for the most part the musical numbers are well done.

There was a rarely experienced moment on opening night as Motormouth Mabel sang her choir-backed civil rights anthem, “I Know Where I’ve Been.” The audience was enthralled and so excited that the applause began to swell before the song was done, then quieted, and swelled again at the climax, literally rocking the roof. The final number, “You Can’t Stop the Beat” elicited a similar rousing response.