Sylvester Stallone’s grimacing killing machine, Rambo, became a symbol of jingoism in the Reagan era, applauded by many Americans and derided by others. Those with a queasy sense of irony even found him funny. In Son ofRambow (so spelled because of trademark difficulties), British writer-director Garth Jennings (The Hitchhiker’sGuide to the Galaxy) would have us believe that the bulletproof avenger was capable of liberating the human imagination and inspiring a generation of young filmmakers. If correct, could this help explain many of the crummy movies made since the 1980s?

Jennings, to be clear, seems to be pleading a special case. The youthful imagination under consideration belongs to Will (Bill Milner), an adolescent in ’80s England whose family adheres to a sect called the Brethren. An especially glum splinter from the Puritan tree, the Brethren’s prayer rooms are as dismal and uncomfortable as their theology; alcohol, movies and television form only part of the roster of prohibitions. Will’s mother, sister and granny go about with covered heads and frumpy long skirts. Dad is dead. Despite all efforts to keep the boy in line, grim regimens of deprivation, when imposed on individuals from without, can often result in push back and even outright mutiny. It must be said that the best-known ex-Brethren was the infamous exponent of sex, drugs and the occult, Aleister Crowley.

Will seeks release from his gray, overcast life in drawing, filling books with colorful magic marker fantasy and producing simple animation on rifled sheets of paper. He ventures into movies at the prodding of a schoolmate, Lee (Will Poulter), who wants to submit his homemade rendition of Rambo to the BBC’s Young Filmmakers Contest. While Will and his fellow congregants form a prayer line outside the local bijou, Lee is inside, eagerly devouring the latest brands of Hollywood junk food.

In school, both are outcasts. Will is nerdy and withdrawn. His teachers must excuse him from class on religious grounds when they show documentaries on the VHS. Lee is a British Bart Simpson, always in trouble and never without a string of apt put-downs. They meet in the hallway when Lee hurls a tennis ball at Will’s face just to see the response. Lee cons and cajoles his nave new companion into becoming the stunt double in his Rambo picture, the actor who endures injury-defying feats such as leaping from the limb of a tall old tree. But while Lee has the chutzpah, Will has the more fertile imagination. Before long the movie’s creative direction is in his hands.

At times visually resourceful, Son of Rambow introduces colorful animation into the live action to bring Will’s inner world to life. With a silly strip of cloth wrapped around his head, the scrawny lad becomes the well-muscled son of the action hero, on a mission to rescue his lost father from evildoers. However, the film’s greatest success is in seeing the real world from a child’s level, not just from the low height of the camera tripod but by capturing the freedom and restriction of adolescence, the sense of drawing from a bottomless pool of time and the constant worry of being bullied by peers and ordered about by adults.

Son of Rambow’s most unique insight comes in the form of a French exchange student, Didier, who sports the latest new wave togs and an implacably blas attitude. He instantly becomes the coolest kid in school, the legislator of behavior, adored by the girls and emulated by the boys. When he decides to become the pint-size Jean-Claude Van Damme of Will’s movie, the struggling production suddenly gains a cast of dozens and all the crew it requires.

Although intended as a comedy of adolescent self-discovery, and generally maintaining its quirky humor, there is an unintended sadness at bottom of Son of Rambow when you consider Will’s choices. He can cling to the joyless Protestant sect of his forbears or free himself by embracing the joyless products of the American entertainment industry by casting himself as Rambo’s spawn. Some of us would call that the horns of dilemma