“Frontline” (8 p.m., PBS, check local listings) spends a thoughtful hour on a subject worthy of months of discussion. “Growing Up Online” meditates on the radical changes in youth culture, education and family life since the advent of the Internet in the mid-1990s.

As the film makes clear, today’s high-school senior has been online since he or she was in first grade. At first, we hear from teachers who find it difficult to teach students who have gotten used to the Web’s culture of instant messaging and immediate gratification.

Some bemoan the medium’s influence on attention spans and worry about plagiarism while others argue that the students are riding the wave of the future and that schools will have to adjust.

We get an overview of the phenomenon of MySpace and Facebook and an adolescent culture of competitive popularity and intimate exhibitionism. Perhaps I’m a geezer, but this is a moment when I wish the documentary would slow down and discuss this shift in attitudes toward privacy. Diaries used to be something young girls kept under lock and key. Now they are exposed for the world to see. When did this change occur and why?

We also see how teens use their camera phones to document and upload drunken and rowdy behavior for all to see. Puke at a concert: Put it on YouTube! Whatever happened to keeping such magic moments to a small circle of friends and sparing the old parental units by the time-honored means of lying and deceit? What’s gotten into these kids?

Several experts interviewed here contend that too much has been made of Internet predators and argue that the teens who find trouble on the Internet go looking for it. We meet a pretty A-student who spends hours on a site where anorexics share information on starving, bingeing and purging and where some worship a figure named “Ana,” the online goddess of anorexia. A far bleaker tale unfolds of an unpopular teen who found “how-to” advice on a suicide site.

Grim anecdotes aside, has the Internet caused a spike in teen depression, alienation, eating disorders and suicide? Or is it merely another way for teenagers to express themselves and drive their parents crazy? An answer of sorts emerges when one authority opines that the Internet has caused the greatest generation gap since the advent of rock and roll.

¢ A repeat “Nova” (7 p.m., PBS, check local listings) from 2006 showcases “A Family That Walks on All Fours,” a film about a members of a large family in remote Turkey who never learned to walk upright. Is their condition a genetic mutation? A step back in evolution? Or cultural in nature? A fascinating hour.

¢ Pickpockets, scam artists and conmen (and women) show how easy it can be to have folks give you their wallet and other valuables on “The Real Hustle” (9 p.m. and 9:30 p.m., Tru).

Tonight’s other highlights

¢ I boldly predict that someone will use the word “journey” on “American Idol” (7 p.m., Fox).

¢ Ryan faces Congress on “The Unit” (8 p.m., CBS).

¢ Cuddy makes an ultimatum on “House” (8 p.m., Fox).

¢ In search of slime eels on “Dirty Jobs” (8 p.m., Discovery).

¢ “48 Hours Mystery” (9 p.m., CBS) looks at a college student at the center of a murder case.

¢ A fertility-clinic break-in leads back to two publicity hounds on “Law & Order: Special Victims Unit” (9 p.m., NBC).

¢ Shirley and Alan take opposite sides of an unusual paternity case on “Boston Legal” (9 p.m., ABC).

¢ “REAL Sports with Bryant Gumbel” (9 p.m., HBO) chats with Reggie Bush’s accuser.

¢ The rich go on blind dates on “The Millionaire Matchmaker” (10 p.m., Bravo). Do they fight over picking up the check?