Four decades ago, a directionless young man named Benjamin Braddock graduated from college, went home, and landed in the clutches of that predator modern taxonomy has dubbed a “cougar.” She was a dangerous crossbreed of hot-blooded desire and reptilian calculation — nature, red in lip and claw. She had killer legs. And she was old enough to be somebody’s mother.

Charles Webb unleashed Mrs. Robinson on the reading public in 1963. The film version of “The Graduate,” with Anne Bancroft in that famous role, followed in 1967. Mike Nichols’s adaptation is full of iconic images, not least of which is its closing shot of Mrs. Robinson’s daughter, Elaine (Katharine Ross), and Benjamin (Dustin Hoffman) staring blankly as a bus delivers them to the great unknown.

What happened next? It may be a question for the kind of person who writes fan fiction or devours Star Wars novelizations, but the cover of Mr. Webb’s new novel, “Home School” (Thomas Dunne, 250 pages, $22.95), promises that the book is the “long-awaited” answer to all our nagging questions. It’s a shame from the get-go. Whether one prefers the ambiguous ending of Mr. Nichols’s film — evocative of the anxiety and uncertainty of a turbulent decade — or the happier one of Webb’s novel, it’s no fun having the story’s grip on the imagination loosened by a sequel. Elaine and Benjamin used to embody a kind of adventurous romance; now they’re smug, self-indulgent — if nevertheless likable — yuppies.

A decade post-“Graduate,” the couple is homeschooling their pair of young boys, Jason and Matt, in Westchester County:

[A] child’s natural learning impulse must be allowed to develop freely, unfettered by direction from above any more than is strictly necessary . . . if this freedom is permitted, innate curiosity will guide the child to the objects of greatest interest and relevance to its life, resulting in an absence of those inhibitions derived from forced institutional learning . . .

Oh, saw you dozing off there. Thought you might appreciate a swift kick in the teeth. Throughout the novel, Mr. Webb alternates between delivering quicksilver dialogue and quicksand exposition, so that the reader never knows whether to chuckle or slip into a coma. The plot is zany but half-baked: Jason and Matt are homeschooled, but the sinister, lubricious principal of their old school wants this to stop, for reasons which never really become clear. The apparent solution is to recruit “Nan,” aka Mrs. Robinson, to seduce the principal so that Benjamin can blackmail him.

Benjamin and Elaine haven’t spoken to “Nan,” or allowed her to see her grandchildren, in years, so this scheme is undertaken in desperation. Having invited the vampire in, so to speak, they find it all but impossible to get rid of her. Her arrival also coincides with a visit, for “moral support,” from a family of appalling Vermonters who are considered leaders of the homeschool movement.

These events all take place sometime around the advent of the garage-door opener, which is hardly the only aspect of “Home School” that feels dated. One hopes that the Braddocks’ hippie-dippy attitudes toward teaching and parenting, which put the children on more or less equal footing with Mom and Dad, has gone the way of the New Math. (There’s even a family policy against locking doors.)

Putting aside these complaints, there is one thing that can thrive on great dialogue, dull exposition, and a preposterous plotline: a screenplay. That’s what “Home School” really is, and the profit motive is as probable a reason for it as any. Mr. Webb and his partner, a woman who calls herself Fred, have endured severe financial hardship, partly because Mr. Webb foolishly signed away his rights to the similarly screenplay-ready “The Graduate,” and that because Mr. Webb and “Fred” have always stayed true to their hippie nature. The Guardian reported that “The couple were delighted when their youngest son, David, now a performance artist, cooked and ate a copy of ‘The Graduate’ — with cranberry sauce.”

And yet, the best and funniest part of “Home School” is not a critique of corporatism and yuppie culture, but rather the book’s relentless parody of the excesses of homeschooling and intrusive parenting. The matriarch of the family from Vermont tries to breastfeed everyone in sight, and to ensnare troubled folks such as “Nan” in a hilariously groan-making New Age practice called a “Circle of Agamemnon.”

If it sounds over-the-top, it is, and I’m afraid there’s just one word for the characters in “Home School”: plastic. At best, they’re something out of a movie; at worst, they’re something lazily adapted from a weird life into a poor book.

The worst parts are the ones Mr. Webb had to make up. The dialogue, though snappy and self-conscious, is at times unbearably contrived, and sounds like nothing if not the sitcom banter of people who know they’re being overheard. Here, Benjamin and Elaine discuss their homeschooling houseguests:

“Publicity seekers you’re calling them now?”

“In a word.”

“Jesus Christ, Elaine.”

“Don’t Jesus Christ me, Benjamin. And their kids are a mess.”

“Oh, let’s rip into their children now.”

“But that’s what you have to look at, Benjamin.”

“And I do. And I find them expressive and involved.”

That kind of back-and-forth, stringing together a series of quickly and cleanly resolved pseudo-problems, is the book in a nutshell. “The Graduate” may be one of the most memorable novels of the 1960s, but “Home School” is a sorry treatment for its cinematic sequel. Until that film does come, courtesy of some shameless and mercenary film studio, we should stick with genuine books and believable protagonists. Otherwise, we’d have to ask whether some shameless and mercenary publishing house was trying to seduce us. It can take a lifetime to live down that kind of embarrassment.

Mr. Beck has contributed to the Weekly Standard, the Wall Street Journal, and other publications.