Plain might be the best adjective to describe “Smashed,” a small-scaled modern retelling of “Days of Wine and Roses” in which Mary Elizabeth Winstead gives an effective, affecting performance as an alcoholic second-grade teacher who tries to break the drinking habit without much help from her slacker husband (Aaron Paul). Despite being about adult characters, it has a certain “after school special” vibe. But although it has a tendency to preach, its homespun honesty helps it work.

Winstead plays Kate, who after a binge causes her to embarrass herself in front of her class and lie to her colleagues, explaining the accident by claiming to be pregnant and suffer from morning sickness, decides she needs help. At the encouragement of his vice principal (Nick Offerman), who has an alcohol problem himself and knows the signs, she begins attending AA meetings, quickly bonding with Jenny (Octavia Spencer, who exchanges the volatility she brought to “The Help” for a sweet maternal warmth), who becomes her supportive sponsor.

But while her husband Charlie (Aaron Paul) doesn’t object, he keeps drinking with his buddies and living a layabout life made possible by the fact that his parents are well off and apparently meet the monetary needs his on-again, off-again work as a writer don’t cover. And as Kate becomes more and more insistent about sobriety, he gets increasingly irked by her attitude, and they gradually drift apart.

There’s a naturalness to “Smashed” that serves it well, with Tobias Datum’s unpretentious cinematography setting off Linda Sena’s gritty production design. But the script adds elements that stray into heavy-handedness. Happily, the performances are good enough to overcome most of the rough patches. The conversations between Kate and Jenny sometimes sound like excerpts from an AA manual, but Winstead and Spencer make them feel genuine. The same is true of a sequence in which Kate and Charlie visit her mother, which Winstead, Paul and Mary Kay Place elevate beyond soap opera status. Less successful is the sequence in which Kate must address her students’ questions about her supposed miscarriage, where the problem of casting non-professional children is all too apparent.

But the scenes with Kate’s campus colleagues register. Offerman adds a pleasantly humorous undercurrent to the helpful vice principal, even selling a delicate sequence in which he ineptly expresses a romantic interest in Kate. And Megan Mullaly brings an offbeat likable quality, and a surprising strain of sternness, to their principal. Winstead also sells the inevitable falling-off-the-wagon scene, and she and Paul bring and unaffected, understated quality to a final scene together, in which they play a game of croquet that’s also one of attempted reconciliation.

With this second feature James Ponsoldt—who co-wrote the screenplay with Susan Burke—demonstrates a knack for clean, straightforward storytelling and a sure hand with actors. Despite some obvious touches, this modest, compact tale of alcoholic’s attempt to change her life has a sense of authenticity and carries considerable dramatic power.