Showing levels of heart, introspection and sensitivity uncommon in today’s frantic fantasy films, “A Monster Calls” is an involving, surprisingly mature tale of pre-adolescent loss, passing innocence and hard-won coming of age. Although it is framed by the story of a schoolboy’s first encounter with real-life tragedy, this thoughtful, cathartic kid’s adventure is as likely to enthrall adults as young people.

Based on the award-winning novel by Patrick Ness (who wrote the screenplay, as well), the film has its hero in a 12-year-old English child trying to hold his collapsing world together. Conor O’Malley (newcomer Lewis MacDougall) is being raised by his single mother (Felicity Jones) with occasional help from his father (Toby Kebbell) following their divorce. Conor is a cartoonist of real promise, inheriting the skill from his mother, who shelved her plans for attending art college to focus on parenthood.

Art is one way we deal with disturbing events in life, and Conor has several to cope with. His mother is increasingly ill, and his rigid grandmother (Sigourney Weaver) overstays her welcome in her visits to help. He’s friendless at his secondary school, where smug older students have begun to insult and physically bully him. Overwhelmed, Conor begins retreating into fantasy, not only through his sketches in class, but in his imagination.

Outside his bedroom window at night he sees a mammoth, fire-breathing yew tree in humanoid form coming his way with menacing strides. The creature, created with outstanding visual effects work and well-voiced by Liam Neeson, is never defined by the film as a real supernatural presence or a frightening daydream. It is not a monster so much as the boy’s strict mentor, telling him folk tales that illustrate the complexities of adulthood, a confusing realm he is fast approaching. The fables are handsomely illustrated in cartoon form, a wonderful conceit that presents nuggets of difficult truth without patronizing or sheltering young viewers.

Director J.A. Bayona, who has skillfully tackled hard material centered on children in the mystery “The Orphanage” and the tsunami drama “The Impossible,” is equally polished here. The film shows how ugly life can be without becoming unbearable. In a wonderful exchange with his father, Conor is told that romantic love isn’t enough to keep couples together, and that most people don’t get happily-ever-after lives. “That’s life, you know?” Dad says. “Most of us just get messily ever after.” It’s a deeply humane sequence that couldn’t be better filmed, written or performed.

MacDougall, with his astonishing wide eyes, and the smoothly skilled Kebbell play seamlessly off each other. Jones and Weaver, each coping with a separate sense of grief, are deeply sensitive without ever descending to sentimentality.

As the monster guides Conor through his difficult journey, the film builds to a climax where it becomes the boy’s turn to share a truth he has long been concealing. While Stephen Spielberg’s recent visit to this territory in “The BFG” was a cute romp, this is an involving story that has something to say. At a time when too many youth-oriented films from Hollywood are filled with cheap thrills, dull plots, unearned emotions and bland characters, “A Monster Calls” brings a bracing air of freshness.

Many parents eager to have their children absorb astute life lessons will doubtless approve. Even without kids in tow, you’d do well adding it to your movies-to-see checklist.