In public speaking and stand-up comedy, it’s a cardinal rule — “Know when to get off.” It’s having the sense to see when it’s time to say, “Well, you’ve been a GREAT audience…” and make your exit.

That’s just as important in movies, knowing when you’ve reached your climax, having the good sense to not to wander into one, two or three anti-climaxes, misguidedly trying to “wrap EVERYthing up.”

That’s a failing of “A Boy Called Po,” a sentimental, sympathetic and fairly well-acted look into the lives of an autistic child and his overwhelmed Dad.

It’s explanatory, showing us what clinicians mean by “regression,” when they say a child on the spectrum is “drifting” — retreating further into his or her own world. And it’s imaginative, offering fanciful speculation on what that child might see and experience in that world inside the mind.

But actor-turned-director John Asher’s warm and fuzzy picture undercuts a big chunk of the goodwill it earns by parking multiple endings after its climax, and beating its sappy theme song — a cover of The Carpenters’ “Close to You” — into our heads, scene after scene.

We meet David (Chrispher Gorham of TV’s “Covert Affairs” and “Two Broke Girls”) at his wife’s funeral. Wracked by grief, how will he cope? How will he explain this to their son?

That’s a big issue, because Po — “Patrick is a good boy’s name, but I think I’ll call you ‘Po.'” — is on the spectrum, 11 years old and mainstreamed into a local elementary school. But his routine has been destroyed, his “Where’s Mommy?” questions won’t stop. He’s added that and “Don’t be afraid, Daddy,” to his list of endlessly-repeated sentences (like his explanation of his name). He is, educators and others start telling David, “drifting.”

Bullied at school, needier by the day, Po (Julian Feder) is derailing David’s airplane-designing career, “regressing.” At least he’s finally found a new classmate to be his friend, Amy (Caitlin Carmichael).

The film’s most inventive touch is where Po goes when he slips into his mom’s room, covers his head in her favorite scarf, and hangs out with Cowboy Jack on the range, Sir Jack the knight in the forest or Captain Jack (all played by Andrew Bowen), a pirate searching for treasure on the beach.

Parents of autistic children may take issue with this speculative “Peter Pan” fantasy (shades of TV’s “St. Elsewhere”). But Julian Feder does a good job at avoiding eye contact, avoiding physical contact and repeating, “Rainman” style, Po’s comfort mantras.

“Mac and cheese, please.”

Gorham is more adequate than dazzling as the lead, and the script has room for lots of TV actors in small, archetypal supporting (Brian George from “Seinfeld,” Bryan Batt from “Mad Men”) roles performing lines that offer no surprises.

It’s a sympathetic portrayal of this disability in a lovely setting, which almost obligates one to cut it some slack. And the script explains away the one groaner of a performance, “Auditioning for an English ‘Wendy’ in ‘Peter Pan'” accent included.

But screenwriter Colin Goldman and director Asher overreach with that conclusion, with no ending “happy” enough to suit them. And that deflates the whole well-intentioned affair.

MPAA Rating:PG for thematic elements and some language

Cast: Christopher Gorham, Julian Feder, Kaitlin Doubleday, Caitlin Carmichael, Sean Gunn, Andrew Bowen, Bryan Batt, Brian George

Credits:Directed by John Asher, script by Colin Goldman. A Freestyle release.

Running time: 1:33