Elevator School

Called an escalator school (esukareitā gakkō (エスカレーター学校) or esukareitā kō (エスカレーター校 or エスカレータ校)) in Japan, an Elevator School is an actual kind of school in Japan and the Philippines consisting of a single institution or (more commonly) a set of sister schools that offer education from elementary or middle school (or even kindergarten) all the way to the university level.

Normally in Japan, elementary school, junior high, and high school are separate institutions, and require prospective students to pass rigid entrance examinations at each transition, as well as when applying to college. Elevator schools, however, allow students to move to the next educational level (junior high, high-school, college) without having to take the standard entrance exams. (In particular, they allow students to bypass the notoriously hellish high-school entrance examinations.) Ironically, elevator schools often themselves require students to pass an examination to gain admission.

In most countries, this is simply what the public school system does, taking in any and all students of the appropriate age living in a defined geographic area. Japanese elevator schools, however are almost all private schools and they are typically very expensive and prestigious, so expect the student body to display Luxury Tropes.

Note that it's entirely possible to flunk out of these schools.

Narratively, this provides a quick and easy way to realistically have characters of very different ages in the same school-like setting. Ironically, not a trope necessarily used to explain away lazy students. Not to be confused with Wayside School, where nobody uses the elevators anyway.

Anime and Manga
The Other Wiki has a short list of examples.
 * Ohtori Academy in Revolutionary Girl Utena teaches kindergartners through at least high school.
 * The CLAMP School, the main setting of CLAMP School Detectives and making a cameo in X 1999, includes all grades from kindergarten through college.
 * As does Horitsuba Gakuen, the school in the Tsubasa/×××HOLiC Omake and CD dramas.
 * Mugen Gakuen (Infinity Academy) and T.A. Girls' School in Sailor Moon. The former acts as a cover for the villains of the third arc and is rarely seen acting as an actual school (though it is one) and is destroyed in the arc's climax. The latter is attended by Rei Hino (a.k.a. Sailor Mars) and is again rarely seen except in the manga side-stories. T.A. also happens to be a Catholic School run by nuns. Rei also comments that while she doesn't have to do an exam to enter high school doesn't mean she has it easy as the nuns could easily not let you pass to the next year if they don't like you.
 * T*A Girls' School is based on the Real Life escalator school Toyo Eiwa Jogakuin, although the real-world school is Methodist rather than Catholic.
 * Mahora Academy in Mahou Sensei Negima is an elevator school (starting from preschool), but a condition of Negi's continuing employment (and thus receiving his magic license) is that he must get the class exam averages up—specifically those of the five worst students, the self-proclaimed "Baka Rangers".
 * Ouran Academy in Ouran High School Host Club.
 * Saki Girls School in Girls High
 * Eriol Academy from Angelic Layer.
 * The Sakurakaoka Academy in Kamichama Karin seems to have at least an elementary branch and a middle school branch.
 * Gakuen Alice from Gakuen Alice is one of these.
 * The Ayanoi Gakuin in GA Geijutsuka Art Design Class is a more realistic example. It has a junior high, a high school and technological university in adjacent campuses, and they share a lot of common facilities—the main characters, which are in the high school, often goes to the university campus to have computer graphics classes and sometimes even for vending machines. It's also worth noting that because of the university's background, the high school have a relelatively large technical/vocational division, on top of general ed and arts divisions—and it's not an Elaborate University High, but just Truth in Television in Japan.
 * Supposedly Hakuou of Hayate the Combat Butler is one, but since all the characters are in high school, you can't really tell.
 * Sakashitamon Academy in Ai Kora.
 * Oujou in Eyeshield 21, but played with using the Poseidon's school, a building so tall and with such tall people that most of the students go on to become elevator workers.
 * Higurashi no Naku Koro ni has got a variation: The school is a small country school, with just one class but still having children of varying ages.
 * Mariasama ga Miteru's Lillian Girl's School runs from Kindergarten to University. It's mentioned that most of the cast have attended for their entire school days with two flashbacks to Kindergarten (one for Sei, Youko and Eriko and another for Sachiko) and Sei attending the University, though she had to take the entrance exams because she was late getting her paperwork in.
 * Youko transferred to Lillian in Middle School.
 * The school attended by the cast of Kimagure Orange Road is specifically mentioned to be an Elevator School in the first episode. Its an extreme example, with classes from Kindergarden straight through high school graduation, and some community college classes.
 * Slam Dunk: Kainan is an escalator school, as it's always introduced as Kainan University Affiliated High School.

Comic Books
"Mrs Drake: I'm sorry what exactly do you teach? Logan: ...Art."
 * Xavier's School for Gifted Youngsters/Xavier Academy, in the comic book, cartoon and theatrical versions of the X-Men. Xavier's "elevator" goes one step higher, since most of the instructors are former students who seamlessly moved into their new roles.
 * Remember that this role is teacher-slash-superhero. Well, in most cases, anyway; it's hard to imagine Wolverine teaching anything but gym. And you do not want him teaching you gym.
 * From X2:


 * Wolverine taught close-quarters combat at the Xavier Institute and continues teaching it, along with history, at the Jean Grey School.

Film

 * Rushmore academy from Rushmore appears to be one of these, as it includes an elementary school in addition to a high school.

Literature

 * The high school in the California Diaries spin-off of the Babysitters Club becomes one of these, due to overcrowding in the elementary school.

Live-Action TV

 * The school in iCarly is a combined Middle School and High School, unusual in a major American city, presumably because the main characters were in 8th grade in the first season and the producers didn't want to cast new teachers and build new school sets after just one season. Justified, in that many school districts in Washington State (the show is set in Seattle) have ninth graders attend junior high, yet take high school level courses and earn high school credit. Apparently it prevents overcrowded high schools. It's also more analogous to Japanese high schools/junior highs, by pure coincidence.
 * It's called a Junior High (in Canada at least).

Video Games

 * In the video game Final Fantasy VIII, each of the three Gardens is an Elevator School (you can get in as early as 5 years old, and you get kicked out if you're not a SeeD by 20), in addition to being an Elaborate University High (some towns have smaller populations than the Gardens).
 * Bullworth Academy from Bully, in addition to being an Elaborate University High, has everyone from kindergartners to high school seniors.
 * Gunjou Institute is this without the university.
 * Escape From St Marys: Though most of the game concerns high school, the entire school has children aged 6 to 18. So though you are a student, you spend time "minding" a younger class and even throw a tiny younger student over your shoulder.

Web Original

 * The Collegium Caelum in Dept Heaven Apocrypha teaches preschool through grad school. Most people transfer in because of scholarships, though, because the cost of actually going to the school from ages six to twenty-six is exorbitant.
 * Super-Hero School Whateley Academy in the Whateley Universe is one of these. Most mutants manifest around fourteen and start as freshmen, but some manifest earlier, so the school has kids as young as eleven or twelve, like Diz and Clover. And it teaches classes that include college and grad school level curricula because some mutants have the brain power, or at least the skills with physics and biology.

Real Life

 * Truth in Television: some American Private schools (usually of the Religious type) and some rural public schools are small enough to have a K-12 range of students.
 * Also in Japan, where many private universities have high schools and junior highs in adjacent campuses.
 * Before the 20th century, due to limited transportation, the need for children to help their parents out on the farm, and the lack of teachers, especially in the frontier, most schools of the era had a dizzying range of age for the students.
 * Those are also common in Mexico today. The Instituto de Ciencias in Guadalajara, for example, has all grades from kindergarten to high school. If you stretch it a little bit, you might consider the ITESO—founded by priests from the I de C -- as part of the campus (and indeed they have a "direct pass" if your GPA is higher than 85%), thus technically making it the same school from kindergarten to doctorate.
 * One has students from 4 to 18 with three adjacent campus: One for preschool, one for the 4 first years of elementary school, the last a big campus for all the others grades. High school classrooms were close to the entrance, Middle school a little farther, Junior School classroom much further... Done to remind students how many years they will have to endure?
 * Many Marist schools also follow this paradigm. Case in point: Instituto México and Colegio México, which begin at elementary school, move on to junior high, high school, and get automatic pass to college. While students do need to change campus, there are no entrance exams as long as they remain within the system.
 * ITESM, also known as Tec De Monterrey, is an elevator school between tenth grade and university, all in the same campus. You only need to take entrance exams for the level you're first applying to.
 * Certain schools - both state and private - in the UK also resemble this.
 * Most secondary schools in England and Wales go from Year (Grade) 7 to Year 11, sometimes with a college or sixth form taking students up to 18 years old included. A small number have primary and junior schools as part of the school. So in all you can have people ranging from 4 years old to 18 in the same school (but probably not in the same building.)
 * Also, the US equivalent of kindergarden to 2nd grade and 3rd to 6th grade are divided into Infants and Junior schools, which are separate educational establishments with their own administration and budget but are almost invariably sited in close proximity and sometimes share certain facilities. The effect is much the same from a pupil's point of view. And then there's certain counties that have a three-tier system that mostly corresponds with the US system, and they usually have at least two out of three tiers co-located.
 * Rural regional schools in Australia often have a small student body, so most schools go from CPC(preschool) to year 12. Many private/religious schools also do this.
 * Australian schools as a whole are like this. Instead of splitting into 3, primary, middle, high school, the vast majority of students will go through a single school from Kindergarten to Year 6 or 7, and then move to a high school for Year 7 or 8 through to the final Year 12. The only formal exam to progress in most states is in Year 10 (Called the School Certificate in NSW). There is a final set of tests in Year 12, but students leave regardless, and would usually go to the equivalent of a Community College if they failed Year 12 but wanted to complete it anyway the year after.
 * One school in Melbourne ran a bit more unusally. Prep - year 8. The 7/8 were the 'high school' section, of an otherwise normal primary school.
 * Pine View School in Osprey, Florida, a public gifted school that ranges from 2nd to 12th grade, all on the same sprawling campus.
 * The Escuela Nueva Laboratorio (New Laboratory School) in Costa Rica has only 1 30-student class in each grade going from preschool (called "5 years" the kids age at the time) to the 6th grade (12 years). The graduates can continue to Liceo Laboratorio Emma Gamboa (Emma Gamboa Laboratory High) which has 3 classes per grade, that never change throught 7th grade to 11th (there's only 11 grades in Costa Rica)
 * The Moravian Academy in Bethlehem, PA. The school also has an association Moravian College which is nearby.
 * In Detroit, there was a campus that included an Elementary School, Middle School, and High School on the same property, though in seperate buildings. It was one of the many places that have been shut down in the city's recent budget-induced closings over the past few years, though.
 * The way the Venezuelan educational system is made means that the most common type of public school is a "Unidad Educativa Básica" (Basical Educative Unit), who teach what is known as the "basic cycle", ranging from ages 5 to 16, and grades 1st-9th. Some UEB have kindergartens, but that's not common outside of big cities. There are also the ones popularly known as "Liceos", who teach grades 7-9 plus the two-three years of "ciclo diversificado" or "Bachillerato" (the equivalent of other countries High School, but with differentiated programs for science, humanistic, and vocational instruction). And there are institutions like the Gran Colombia School, who has all the range from kindergarten to Bachillerato, with a technical vocational school and (more recently) a college trown to the mix.
 * In the Philippines, it's not uncommon for universities to have high schools, elementary schools, and even kindergartens attached, usually in the same general area. Also, one university (such as De La Salle University or St. Scholastica's College) may have different campuses (and adjacent high schools...etc.) all over the country.
 * Tends to happen in college towns in the US too; just for example, the University of Arkansas has an elementary school and a combined middle and high school (same campus, different buildings) all within walking distance of the main university campus, in addition to several daycares. They aren't the only schools in the area though.
 * In Denmark, the normal public school system works like this; going from kindergarten classes to 9th grade.