After two unsuccessful pregnancies, Elaine Hall travels to Russia to adopt a child. At an orphanage there, she meets a 23-month-old boy, and it is love at first sight. A camcorder captures the soon-to-be mother and son cuddling and cooing. But shortly after they arrive in America, the youngster, Neal, begins to exhibit troubling behaviors. He runs in circles and throws violent tantrums. His speech is severely impaired, and he sleeps only two hours a night. The diagnosis: autism.

When Neal is 12, Ms. Hall, an acting coach and educator, decides to cast in a musical a dozen autistic children, including her son, who almost never speaks. Since children with autism can have difficulty forming attachments, getting a group of them to take the stage as part of an ensemble cast is a colossal undertaking. The 22 weeks of preparations for the climactic performance provide the narrative arc for “Autism: The Musical,” a documentary by Tricia Regan that has its small-screen premiere tonight on HBO.

The 90-minute film airs on the heels of a high-profile case, in which the federal government acknowledged that a series of vaccinations might have contributed to the impairments of a 9-year-old autistic girl. The government agreed to compensate the girl’s family but did not waver from its position that vaccinations are not linked to autism, which comprises a spectrum of developmental disorders thought to afflict one in every 150 children. In “Autism: The Musical,” tumultuous rehearsals supply the dramatic tension inherent in performance documentaries. Ms. Regan uses the lead-up to the staged musical, undertaken by Ms. Hall’s Miracle Project, as a way to tell a larger story. Most of the screen time is devoted not to the show’s preparations, but to the daily lives of five of its cast members — Neal, Lexi, Adam, Wyatt, and Henry — and their families, who exhibit a humbling commitment to enriching the lives of their challenged children.

We observe as parents attempt to enter their child’s mysterious and seemingly locked world. “If he would spin in circles, we would spin in circles; if he would stare at his hand, we would stare at our hands,” Ms. Hall says of her early efforts to connect with Neal.

We see, in home videos, a smiling Lexi, who as an infant seems to be developing on schedule; then we see her transform into an unresponsive toddler who spends hours rocking back and forth and who seems not to notice when her parents call her name. By the time her sweet singing voice lands her a solo in Ms. Hall’s production, she is a 14-year-old who can echo what others say, but has trouble verbalizing ideas of her own. Lexi’s mother tells the other Miracle Project parents that her daughter’s school seems determined only “to train her so she can push a broom across McDonald’s. I want the world to value her and they don’t.”

We watch as marriages become strained and broken by the stress of raising an autistic child. Neal’s parents divorced years ago; Lexi’s parents separate during the course of the film. We learn that 9-year-old Adam’s father, Richard, began an affair the month his son was diagnosed with autism. “You see an awful lot of single moms of autistic kids,” Richard says. “There are many reasons men leave women, but women may overlook that they may have been a factor … by being so monomaniacal, so self-involved with their kid. The world revolves around them getting that one last ounce of information to apply to their kid’s environment or learning, or whatever.”

Ms. Regan gracefully weaves interviews with parents — and with 10-year-old Wyatt, who is among the most articulate of the Miracle Project participants — with footage of the children at home, in school, and on the beach, and with that of the youngsters preparing for their musical debut. During rehearsals, she captures their breakthroughs both small (sitting in a circle, making eye contact when speaking, shaking hands with a peer) and large (role-playing, committing lines and lyrics to memory).

There is no voice-over narration chiming in with statistics about the prevalence of autism; no physicians present to explicate its symptoms; no behavioral therapists to suggest treatments, and no scientists weighing in on vaccination theories. As a result, viewers, who by the end of the film have come to root for the children and empathize with the parents, may be left with the most basic of questions: What is autism?

The film’s subjects, after all, include a child who can describe aloud his awareness of his own isolation, and another who does not speak, save for a few guttural sounds. There are those who long for round-the-clock playmates, and those who prefer solitary pursuits of narrow interests. (Ten-year-old Henry, diagnosed with Asperger’s syndrome, a high-functioning form of autism, spends almost all of his spare time studying reptiles.) And then there are those for whom peer interactions can quickly turn violent. Some of the children have been integrated into mainstream classrooms, performing more or less at grade level, and others spend their days in special-education courses, learning life skills such as washing dishes and crossing the street.

These children seem to have little in common besides an aversion to eye contact, an outsider status on the playground, and a foggy diagnosis of autism. The range of cognitive function, communication skills, and impulse control shows that autism is not a monolithic disorder that condemns people to “standing in the corner, banging your head against the wall, you know, in a diaper,” as one mother of an autistic daughter feared upon hearing the diagnosis.

“There are all these myths about what a child with autism can do,” Ms. Hall says, discussing the musical in the film’s opening scene. “I plan to shatter those myths.”

But the chaos that ensues at the temper tantrum-filled dress rehearsal, during which Adam goes temporarily missing, instills doubt that Ms. Hall and her acting students can ultimately pull this off. What we see of the performance, two days later, is so seamless and satisfying that viewers might wonder what sorts of crises littered the cutting-room floor. In the end, the curtain call is the filmmaker’s resolution to a story for which there remain many more questions than answers.