High school may be the best four years (or nine seasons) of your life, but it can't last forever.
Glee, whose fourth season premiered Thursday night, is at a crossroads. The once-revolutionary musical comedy-drama has alienated most of the critics (and, judging by its falling ratings, some of the viewers) who at first rallied around its quirky storylines and underdog characters. Perhaps that's why, during May's upfronts, creator Ryan Murphy announced that the show will be a bit different this year, splitting its focus to both remain at William McKinley High and follow some newly graduated characters to performing arts school in New York. While we hope Glee will get it together in Season 4, we think it's only fair to provide viewers with a (spoiler-filled) guide to spotting a teen TV show that has exceeded its expiration date.
1. The main characters have graduated from high school
Sorry, Glee, but in our estimation the number-one sign a teen TV show is headed for obsolescence is graduation. Take Veronica Mars. After two fantastic seasons, the cult girl-detective series opted to split the season into two ongoing mysteries in a misguided attempt to attract more viewers—and added two shrug-worthy characters in Veronica's college classmates, Parker and Piz. The quality nosedived once Veronica moved on from Neptune High, with its evil rich kids and sinister class divisions. But Veronica Mars is hardly the only show that lost its touch when the characters moved on to college. Remember Beverly Hills, 90210 around the time Dylan meets his faux little sister and Ray Pruit shows up? Need we even go into the specifics of Saved by the Bell: The College Years?
2. Every possible couple has been exhausted
Gossip Girl should have known it would need a larger cast of regulars to support its level of bed-hopping. When Blair has already dated Chuck and Nate; Dan has tried to make a go of it with Vanessa, Serena, and even Georgina; and even little Jenny has freaked us out by kissing Nate and losing her virginity to Chuck, her would-be rapist, the couples stop making sense. That's when we get mismatches like Dan and Blair, and Vulture has to go and make an interactive chart of who's fooled around with whom. But while Gossip Girl is perhaps the most egregious example of this tendency, plenty of other teen TV shows have fallen into the trap, from That '70s Show to Saved by the Bell to Beverly Hills, 90210.
3. The lead cast members have left the show
Speaking of things 90210 and That '70s Show share, both kept on going after they lost lead actors. In the case of the latter, Topher Grace and Ashton Kutcher declined to return for the retro sitcom's eighth and final season, leaving the show without its protagonist and comic relief/eye candy—not to mention its two biggest stars. Josh Meyers' Randy Pearson was cast to fill the gap, but the fact that we had to Google to find that character's name speaks to how effective that substitution turned out to be.
Shannen Doherty, meanwhile, left 90210 after only four seasons amid reports of on-set tension, and the remainder of the series' ten-season run was marred by futile attempts to replace Brenda Walsh. First we got Valerie, then we got Gina, but those bitchy brunette newcomers could never match Brenda for neurotic, teenage relatability.
4. Subpar minor characters become series regulars
Things were getting pretty desperate for The O.C. by the time it killed off Marissa Cooper (resulting in the departure of Mischa Barton, a casting change that made it yet another teen TV show that lost a lead actor). But nothing portended its doom more than the promotion of Marissa's younger sister to the status of a series regular. When we met Kaitlin Cooper, in Season 1, she was a horseback-riding innocent who eventually disappeared to boarding school, played by Shailene Woodley. By the time she resurfaced midway through Season 3, she had been transformed into Willa Holland and was just as conniving and debauched as everyone else on the show—which was a convenient, if totally disingenuous, way of transforming her into the new Marissa. See also: Gossip Girl, which shares a creator with The O.C. in Josh Schwartz and attempted to breathe life into Blair's cardboard cutout prince, Louis, because (once again) there was nowhere else to go after her millionth break-up with Chuck.