Fifty-five years ago this week, Theodore Cleaver had a big problem. His teacher had assigned him to write a 50-word essay about his mother, June, but after interviewing her he found that her life had been numbingly unexciting.  “Once at summer camp I won a blue bathing cap at swim meet,” June told him, searching desperately for something scintillating.  Television matriarchs have changed quite a bit since that Season 3 episode of “Leave It to Beaver.” Take the ones on the CBS series “Mom,” which ends its eventful second season this Thursday. Bonnie (Allison Janney), who has logged a lot of time in prison, has fallen off the sobriety wagon, hard. Her daughter, Christy (Anna Faris), who is also in recovery, recently gambled away the rent money. And a few months ago her daughter, Violet (Sadie Calvano), gave a newborn up for adoption. Are you getting all this down, Beav?  “Mom,” by the way, is a comedy. When it first arrived on the air in the fall of 2013, it was a relatively undistinguished one, trying to generate laughs by being loud and often vulgar. But midway through Season 1, its creators, Gemma Baker, Chuck Lorre and Eddie Gorodetsky, grew more ambitious.  The show started going a little deeper into its characters’ flaws, which meant talking about things like alcoholism and abandonment and domestic violence. Now the series is a weekly dose of substance, one that stands out in a network-television universe full of nontraditional families and dysfunction. It manages the difficult trick of venturing into seriousness without growing overly maudlin or preachy.  Credit the work of Ms. Janney and Ms. Faris, who are the core of the series. When we first met them — Bonnie re-entering her daughter’s life after a long estrangement; Christy a single mother trying to straighten out — their relationship was defined by shrillness. But Ms. Janney, who won an Emmy for the role last year, and Ms. Faris have since honed their comic relationship and are now as funny as any duo on TV. There is still plenty of “shrill” in this show, but there is also a wealth of “droll” and “deadpan”:  Bonnie: “I’m sorry I called you a bad liar. You’re a great liar.”  Who gets the setup and who the laugh line? These two actresses can work it either way:  Christy (to Violet): “Why are you dressed like a cheap hooker?”  Bonnie: “Yeah, next time you want to borrow my clothes, ask first.”  It’s a classic case of the principal players finding a comfort zone and the show’s writers responding by giving them more and more pithy material. Television comedies discovered a few generations ago that they could go beyond merely stacking cheap gags one atop the other; certain episodes of shows like “All in the Family,” “Maude” and “M*A*S*H” are legendary for springing serious subjects on audiences that tuned in expecting easy laughs.  “Mom,” though, has been doing this with more alacrity than some of its predecessors. It’s not, “We’re going to stop being comical this week and do a breast-cancer episode”; it’s, “We’re going to stop being comical for a minute and a half, then hit you with a brash joke, then be serious for another 45 seconds, then spring another gag.”  That’s a tough assignment for an actress to pull off. On a drama, a brooding cop might nurse a scotch for an entire episode; here, Ms. Faris and Ms. Janney have to sell the serious stuff fast because it doesn’t last long.  The season is ending with an arc pegged to Bonnie’s relapse, which came via a back injury a few episodes ago. That injury gave Ms. Janney, one of the most interesting actresses working today, a chance to showcase some physical comedy that was as funny as anything Lucille Ball ever did. But all of her writhing around on the floor was in service to a plotline in which Bonnie became addicted to painkillers.  The fall from grace has jeopardized Bonnie’s relationship with Christy and practically everyone else in her life. That includes the other members of the Alcoholics Anonymous group both women attend, some of whom have become significant characters as the series has progressed, all with side stories that give the show other serious subjects to explore.  Although there are men in “Mom,” this is an almost all-female show, the polar opposite of the near invisibility June Cleaver and the other early-TV moms were relegated to. These days, if there is a vacuous parent on a sitcom, it’s likely to be a father. The dad on “Fresh Off the Boat,” for instance, is not exactly a font of “Father Knows Best” wisdom.  Back in 1960, Beaver feared that his mother’s bland résumé would get him laughed at when he read his essay aloud in class. So he sexied her up a bit by borrowing the life story of an actress he overheard being interviewed on television. The mom of his “Mother’s Day Composition” was a dancer who worked in chorus lines and dive bars until a gangster took a liking to her.  When Beaver read that essay, his teacher’s head practically exploded. But the kid was simply ahead of his time. Today, while June Cleavers have become extinct on TV, the mother Beav made up would have fit right in on “Mom.”  A version of this review appears in print on April 30, 2015, on page C1 of the New York edition with the headline: Issues That Go Beyond Kissing Boo-Boos. Order Reprints| Today's Paper|Subscribe
As Season 2 draws to a close, the show has grown from an undistinguished sitcom to one that stands out for its substance.