Ah, that one summer when everything changed.

Hollywood loves Summertime Coming-of-Age Movies (SCOAM). From “Summer of ’42” to “Stand by Me,” from “Now and Then” to “The Kids Are All Right,” from “Dirty Dancing” to “Call Me By Your Name,” from “Crooklyn” to “The Way Way Back,” the SCOAM is a wonderful platform for comedy-dramas where we can identify with the insecurities, restlessness, dreams, romantic triumphs (and setbacks) and madcap adventures of the lead characters, even if their backgrounds are far different from ours.

“Measure of a Man” is just such a film. It’s a sweet and knowing and lovely and funny story, but occasionally the spell of warm nostalgia is broken by painful moments of family heartbreak and cruel bullying.

This is a movie that has us caring about the main characters from the get-go, and that’s a tribute to the direction of Jim Loach, the screenplay by David Scearce (adapting the popular and acclaimed young adult novel “One Fat Summer” by the great Robert Lipsyte), and the terrific cast of talented young actors and likable veterans.

“Measure of a Man” (not a great title; they should have gone with “One Fat Summer” and endured the silly slings and arrows of anyone who would have criticized it) takes place in the summer of 1976, with the Marks family making their annual vacation trek to a resort in the woods.

Fourteen-year-old Bobby Marks (Blake Cooper) narrates the story from an unspecified time in the future, delivering his lines with a polish and wry humor reminiscent of Daniel Stern’s VO work in “The Wonder Years.”

Bobby’s father, Marty (Luke Wilson), is the family member most excited about the summer-long vacation, even though his business ventures take him back to the city for weeks at a time. His mother Lenore (Judy Greer), who recently has become involved in the women’s liberation movement and is going back to law school, dotes on Bobby and his older sister Michelle (Liana Liberato).

Bobby’s a heavyset kid with a wild tangle of curly hair, and a quick and ready wit. Every summer, he reconnects with Joanie (Danielle Rose Russell), his best friend since he was a toddler. They’re both nerdy and smart, and they’ve always felt as if they were on the outside looking in, so they’ve found great friendship and comfort their bond.

Desperate to avoid joining a corny summer camp, Bobby sets out to find a job, which brings him to the palatial summer home and grounds owned by Dr. Kahn (Donald Sutherland), a Wall Street wizard who summers here every year.

Sutherland’s Dr. Kahn wears a straw hat and has a peculiar way of enunciating, because that’s what Donald Sutherland has often done (among many other things) in a half-century of acting: he wears hats like nobody else, and he speaks in a distinctive manner, and he’s great fun to watch.

Dr. Kahn hires Bobby to mow the lawn, clean the gutters and perform other outdoor chores, for the princely sum of $2 an hour — “top dollar,” as Dr. Kahn puts it. (Of course, we know Dr. Kahn will also dispense words of wisdom and offer Bobby life lessons as the summer days grow ever shorter. He’s a classic Summertime Coming-of-Age Movie Mentor!)

It’s a rough summer for Bobby. No sooner does Joanie arrive than she tells him she’ll be going back to the city for at least a month. (I’ll not give away the reason for her trip.)

Bobby sees his mother crying late at night and wonders if his parents are getting a divorce. He resents his sister’s hunky new boyfriend, Pete (Luke Benward), because Pete has no idea what’s it like to be overweight and underconfident. And he’s the target of increasingly vicious and brutal bullying at the hands of Willie Rumson (Beau Knapp), a hot-tempered townie with a dark past.

Against the backdrop of the Bicentennial celebration, with songs such as America’s “Lonely People” and Jonathan Edwards’ “Sunshine” perfectly setting the tone, “Measure of a Man” serves up some predictable summertime escapades but more than a few surprises as well. We learn some truths about a number of supporting characters that put things in a different light.

It’s jarring when the bullying subplot takes a dark turn to the point of criminal assault — and the resolution of that particular conflict doesn’t ring true. But that’s the only plot thread among more than a half-dozen that veers off path.

I’d love to find out what eventually happened to Bobby and Joanie and Pete and even Willie Rumson after that one summer that changed everything.

★★★1⁄2

Great Point Media presents a film directed by Jim Loach and written by David Scearce, based on the novel “One Fat Summer” by Robert Lipsyte. Rated PG-13 (for thematic content including some intense bullying, teen drinking and sexuality, and for language). Running time: 100 minutes. Opens Friday at Facets Cinematheque and the Wilmette Theatre.