Everyone Went to School Together

"Dee: Wait, you went to high school with us?

The Waitress: Yeah, I sat right next to you in Trig.

Dee: Huh. Wow, you are very forgettable."

- Its Always Sunny in Philadelphia

This is when great majority of adult characters knew each other during their school years. This may be revealed in a Flash Back, a childhood spinoff series, or just be mentioned in dialogue.

Not only that, their personalities have gone completely unchanged since then. For instance, all married couples were High School Sweethearts and any mean person is a Schoolyard Bully All Grown Up.

Often, this is used as an easy way to gather a cast. It can result in Writers Cannot Do Math if the characters are previously established to be of different ages, especially if by more than a couple of years.

Subtrope of One Degree of Separation.

Anime and Manga

 * Durarara: Shinra, Shizuo, Izaya, and Kadota were all in the same high school, which happens to be the same school the teenagers are in at the present. Shinra was also in the same elementary school as Shizuo and the same middle school as Izaya.
 * Neon Genesis Evangelion: Ryoji Kaji, Misato Katsuragi, and Ritsuko Akagi all went to the same college. Also, Gendo and Yui were the advisee and favorite student (respectively) of Fuyutsuki. Gendo and Yui get married, and Fuyutsuki becomes Gendo's second-in-command
 * Bleach: Various members of the Gotei 13 went to the Academy together, and its those relationships that end up informing much of the intrigue in the Soul Society Arc.
 * Subverted in Saint Beast, as there is one training academy in heaven and everyone did go there together but realistically only a few of them met during that time because they were learning different disciplines. Their personalities, however, did not change.

Comic Books

 * Marvel Comics and Wildstorm Studios tried doing this during the short-lived Heroes Reborn Re Boot: they had Reed Richards, Victor von Doom, Tony Stark, Bruce Banner, and Hank Pym studying together at the same college, even going so far as to call themselves the "Knights of the Atomic Round Table" before breaking apart. Reed and Doom (and Ben Grimm) all went to Empire State University in the normal Marvel Universe, as well. Peter Parker went there years later.
 * In some versions of Superman, (most notably the Silver Age Superboy stories) Clark and Lex were at school together in Smallville. This is currently canon again, presumably to tie into Smallville (where they weren't).
 * There was a Silver Age story where Batman and Superman went to school together in Smallville. A Reset Button was pressed near the end when one of the characters was hypnotised to forget the other. The fact that it showed Bruce Wayne's parents to be alive and alright was the least of its many, many flaws. This story was later retconned in a late 70s anniversary issue of "World's Finest Comics" (a Roy Thomas written tale summarizing all the various Golden Age and Silver Age "first meetings" of Superman and Batman) to show it was Bruce's guardians, not parents.

Film

 * Part of the premise of the eleventh Star Trek movie, an Alternate Universe/Continuity Reboot prequel in which most of the major original series characters are new Starfleet Graduates who serve together on the Enterprise right off the bat.
 * The setup for The Muppets Take Manhattan is that the Muppet characters all went to college and worked on their senior class musical together.
 * In Young Sherlock Holmes, Holmes and Watson go to school together, and The Stinger reveals that.
 * In the Adam Sandler comedy Big Daddy, several of the film's characters are said to have attended Syracuse University together. Even more improbably, nearly a decade later they're all still hanging out together in the same neighborhood in New York City, which, in case you haven't heard, is one of the most enormous cities in the world.


 * Terminator 3: Rise of the Machines of all things. While it wasn't specific said that all of John Connor's lieutenants went to school with him, it would appear that most of them did. From this we can conclude that the future ran out of professional soldiers and he had to fall back on people he knew for less than a year when he was ten (or thirteen, depending on which film you're watching).

Literature

 * Harry Potter: Justified in the series since there's, you know, only one Wizarding School in Britain. Still, it's a rather interesting coincidence that so many important characters (James Potter, Lily Evans, Sirius Black, Remus Lupin, Peter Pettigrew and Severus Snape) not only knew each other at that age, but were all in the same year.
 * Though it is to a high degree because of their knowing each other that they became important.
 * Wicked is an External Retcon of The Wonderful Wizard of Oz. According to Gregory Maguire's book, Glinda the Good Witch and the Wicked Witch of the West (plus her little sister) all went to the same school. In the musical, . In the British version, Glinda lampshades this with an exasperated, "We were all at Uni together ..."
 * Soon I Will Be Invincible: Played surprisingly straight (and given a small lampshade). Dr. Impossible, CoreFire, Blackwolf, and Damsel went to the same school, and mostly knew each other; however, it was a school for the intellectually gifted and they weren't all in the same year. (Also, it eventually turns out that .)
 * Wing Commander: A lot of named characters in the novels tend to get this, though usually it's more that they knew each other from previous commands while serving in the military, not from schooling.
 * Stranger Than Fiction the Life And Times of Split Enz shows that the entire band, with the exception of latecomers Malcolm Greene, Nigel Griggs and Paul Hester, all knew each other from either the same high school or the same college, even if they didn't always go at the same time (e.g. Neil).

Live Action TV

 * Buffy the Vampire Slayer: Out of all the opening credits characters in the Buffyverse, only four (Tara got in opening credits once, but if she didn't, I'd still count her) of them were not either working at Sunnydale High, somehow able to be in Sunnydale High 24/7, Working with the Scoobies while they were in Sunnydale High, had entered Sunnydale High multiple times or going to Sunnydale High. Even Angel's secretary in Season 5 is the former Cordette and Ex-Girlfriend of Spike, Harmony. That's what happens when you go to school on a Hellmouth.
 * Most of the Time Lords you will meet in Doctor Who know each other, and at least the Doctor and the Master and the Rani went to school together at the Time Lord Academy and were taught by Borusa. The Time Lord Academy is described as a stuffy British public school type of place with different houses (the Doctor and the Master were Prydonians) and classes on cosmic science and the like. It seems to award British-style university degrees (the Doctor barely scraped past on the second try, while the Master always got better grades and even his degree was higher). Just never, ever compare it to Hogwarts in front of an old series fan.
 * In the Doctor Who Expanded Universe some of the writers (namely Gary Russell) decided all of the famous renegade Time Lords (including the War Chief, the Meddling Monk, et cetera) went to school together and even had their own school clique. New series fans seem to cheerfully accept this as canon without questioning or even having read said novel, especially if the concept can be used as Fanfic fodder.
 * On Wings, the characters not only went to the same high school, they all had their reunion together, despite being different ages. This was Handwaved by saying the school was too small for individual classes to have separate reunions.
 * Semi-averted on The Steve Harvey Show as Lovita did not meet the rest of the cast until she started working at the school. Steve and Ced were college roommates. Steve and Regina have known each other since childhood. However, later episodes imply that Ced and Steve and Regina attended high school together.
 * This is how the cast of The Class are gathered. The main character, who first met his current girlfriend back in third grade, decides to throw a party and invite all their former classmates from that year. The main cast consists of a handful of the ones who establish/re-establish relationships, and happen to all still live in the same city.
 * Veronica Mars:
 * Veronica's mother went to school with Love Interest Duncan's mother and father: explored in "My Mother, the Fiend" and a plot point in other episodes.
 * Veronica's teacher and Trina's mother. They all seemed to be in the same year.
 * This is how the 60% of the cast of How I Met Your Mother got together. Ted and Marshall were roommates at Wesleyan, and Marshall started dating Lily when they were all freshman. Marshall and Ted kept up the roommate thing when they all moved to New York.
 * In The George Lopez Show, George and Angie are High School Sweethearts, and George's best friend Ernie also went to school with them. The principal of Carmen's school is also seen to be a bully all grown up.

Video Games

 * This was a Twist, Plotpoint and Reveal in Final Fantasy VIII.
 * In Tales of Symphonia, half of the final party either attended the school or taught at it.
 * In the Silent Hill series, Alessa, Walter, and Claudia all knew each other as children because they were all part of the same cult.
 * Happens in Super Robot Wars on occasion, usually as a matter of narrative convenience. For example, the recent Super Robot Wars Z2: Hakai-hen combines the school plots of Gundam Wing, Gundam 00, and Code Geass all together so that characters like Heero and Saji attend Ashford Academy.
 * The three protagonists of "Supreme Commander 2'' all went to the same (presumably international) academy together. Surprisingly, none of them are forced to fight one another during the new war; instead they all band together against the real antagonist who is stirring up trouble.

Web Comics

 * In Elf Blood, given that the main institution of the story, The Council, has an academy that raises soldiers from elementary school age through high school and beyond, it's not that surprising that many of the main characters have gone to school with one another.

Western Animation
"Hank: You are not gonna tell me that you went to college with the Monarch, too! Where did you guys go, Super Crazy No-Way School?!?"
 * The Venture Bros: Pretty much every single important adult character went to college together: Dr. Venture & Brock (roommates), Pete White & Baron Underbheit (roommates), The Monarch, and one-off villain Mike Soriyama. This was lampshaded by Hank when the person relating the story mentions "the weird kid with huge eyebrows who's obsessed with butterflies".


 * Phantom Limb and Professor Impossible taught at that same college, Dr. Girlfriend was a student there (though she didn't attend at the same time as the previous group), as was Billy (though he was undercover to spy on Phantom Limb). Even Monarch Henchman #21...
 * On Camp Lazlo, Everyone Went To Camp Together. Lumpus and Slinkman, anyway, and Jane went to the girls' camp on the other side of the lake.
 * Kim Possible: Every guest scientist of the episode that isn't old and gray can be assumed to have gone to college with Kim's dad. This includes arch-foe Dr. Drakken (aka Drew Lipsky, who didn't actually graduate).
 * The Flintstone Kids features Fred, Barney, their future wives, and even Fred's future boss, all attending elementary school together, but in the original series (and the 2000 live action movie) Fred and Barney did not meet Wilma and Betty until they were in their 20s, just after graduating from college.
 * The Flintstones: Fred and Barney dated Betty and Wilma late in high school (which became the focus of one episode involving an old love letter of Fred's). One episode also shows Fred never having graduated from high school, let alone gone to college (though another episode had him enroll in night classes at "Prinstone").
 * The CGI Iron Man cartoon features Tony Stark as a teenager who attends the same high school as James Rhodes and Pepper Potts, his future employees.

The Big Bad and another of his Rogues Gallery members are also students there, though this is mostly justified as the rogue in question chose the school so she could be close to Tony. ""We're suspicious of any high school that produces no fewer than 12 supervillains in one graduating class, but admittedly it does put an interesting spin on those Council of Doom meetings to think they're really just high school reunions.""
 * The Simpsons: In the episode "Springfield Up", most of the middle-aged adult characters are seen as kids, going to the same school -- including Homer and Marge.
 * "Gotham High", a show that never got beyond the development stages, had a young Batman in the same class as every villain in the franchise. Needless to say, Cracked had a field day with this:

Real Life

 * From 2007 to 2009, three alumni of James Madison High School in Brooklyn, New York were all serving in the United States Senate at the same time, from three different states. They were Chuck Schumer of New York, Norm Coleman of Minnesota, and Bernie Sanders of Vermont (Sanders and Schumer continue to serve together to this day). Other prominent former students of that particular high school include Supreme Court Justice Ruth Bader Ginsburg, stand-up comics Andrew Dice Clay and Chris Rock, and Nobel Prize-winning economists Gary Becker and Robert Solow.
 * Phillip Zimbardo and Stanley Milgram, the two most notorious experimental psychologists of all time (Zimbardo for the Stanford prison experiment, Milgram for the Milgram shock experiment), were buddies in high school.
 * Many New York rappers who came to prominence in the 1990s either grew up around each other or literally went to school together. Notably, Jay-Z, The Notorious B.I.G. and Busta Rhymes often found themselves battling each other at lunch time.
 * Many of the big name Generals during the Civil War were all from West Point, regardless of their affiliations with the Union or the Confederacy. The West Point class of 1915 was nicknamed "The Class The Stars Fell On" because so many members, including Dwight Eisenhower and Omar Bradley, would become famous generals during World War II.
 * A popular criticism of the current government of the UK is that both the Prime Minister and the Chancellor went to Eton.