It’s rather astonishing that this little movie, which Harry Potter’s chum Ron Weasley, also known as Rupert Grint, made in the interval between the latest installments in that mega-franchise, is as pleasant as it is. After all, though “Driving Lessons” is a semi-autobiographical piece by Jeremy Brock (who also directed), the tale of a retiring teen who’s liberated from the stifling orbit of a demanding parent through an eventful road trip has a lot in common with “Ferris Bueller’s Day Off,” with Grint as that film’s Cameron. Added to the mix is that the parent is his waspish mother, who’s also unfaithful to his laid-back, distant father–a device reminiscent of “The World of Henry Orient.” And as if all that weren’t enough, the Bueller figure this time around is a wild, extravagant older woman–it’s “Auntie Mame” time. But somehow this weird mixture works.

Grint plays Ben, a shy, bookish teen, the son of a put-upon Anglican clergyman (Nicholas Farrell). Both are under the thumb of Laura (Laura Linney), Ben’s self-righteous, imperious mother, who feigns uprightness but meanwhile uses her son to cloak the affair she’s having with her husband’s young curate (Jim Norton). When she takes an elderly man who’s just lost his wife into their home as an act of self-promoting charity, she suggests that Ben might get a summer job, and he does, as general factotum to an elderly actress, Evie Walton (Julie Walters), an endearingly eccentric old lady who both orders him about and urges him to find himself. Ultimately she tricks him into driving her to Edinburgh for a poetry reading though he doesn’t even have a license, and there he has his first sexual encounter, though it unfortunately leads to his failure to meet his obligations to Evie. After he returns home, his mother–furious that he went on the trip without her permission–orders him to have no further contact with the actress, but ultimately she and Evie will confront one another over his soul, and Ben’s father too will have to rouse himself in the face of his wife’s infidelity. It goes without saying that in the end Ben will find his way through the thicket of family troubles and learn to make his own choices.

There’s not much new in all this; although Brock’s script is supposedly based on his own experiences one summer with Dame Peggy Ashcroft, it greaty resembles previous movies like those mentioned above, and some of its subplots–like the one involving that elderly houseguest–don’t come off. But in this case familiarity doesn’t breed contempt, because the cast is so winning. Walters is an adept scene stealer, effortlessly making even Evie’s brashest conduct amusing, and she handles the inevitable tear-jerk moments well, too. In Grint’s hands, Ben can seem a bit neurotic, but he remains an endearingly klutzy fellow. And Farrell does a good job as his wimpy father. Linney has a more difficult time playing his mother; she tries to alleviate the brusqueness with a hint of vulnerability, but as written the role still has an element of plastic villainy to it. The rest of the cast is okay if not outstanding, and technically the movie is modest but solid, as befits a picture made by a group calling itself Rubber Tree Plant Productions. High hopes, anyone?

The makers of “Driving Lessons” may have learned a bit too much from previous movies, but they’ve put the results to pretty enjoyable use. Their effort may not go to the top of the class, but it earns a low pass.