American kids, as part of their health ed' class, often have to take care of an egg for a while and treat it like a child. If the egg is broken at the end, or they don't have somebody always looking after it, they will fail. Curiously, this is never run by other teachers at the school, who are less than sympathetic when it interrupts their classes. Usually, the kids are paired for the assignment, but sometimes each individual kid has their own egg.
Usually, the kids are totally irresponsible, and will either play catch with the egg, fight over it, lose it among several hundred other eggs, or otherwise risk flunking. Hilarity Ensues. Often, when the students are paired, the main character will have to work together with someone he or she doesn't like — or may have another kind of tension with — to get themselves out of the mess they put themselves in.
Often the egg breaks and they replace it with another one, only to be found out because the teacher had secretly placed a pencil mark on the egg.
This trope is also semi-common with teenaged superheroes, who must then try to fufill the assignment while keeping up with their crime-fighting.
This is something that Real Life high schools actually do to discourage students from having unprotected sex, the moral being: "Look at what a pain it is to take care of a kid at your age."
In the real world, the eggs have mostly been displaced by lifelike dolls, equipped with features to make them even more annoying, like a battery-powered chip which makes the baby scream. Only some Egg Sitting episodes have made the switch. Occasionally a third option is used. A bag of flour or sugar, for instance, which more properly imitates the weight of a baby.
Note that this is a very specific trope to the US (and perhaps Canada) and when it is encountered by others in American-made media, a common response is to think it an example of Aluminium Christmas Trees.
Subtrope of Parents for a Day. Compare Egg McGuffin, the more literal version. When the pretense is replaced by madness, that's Baby Doll Baby.
In License To Wed, the couple being tested by Robin Williams's character are given a pair of extremely disturbing baby dolls. In addition to being equipped to scream and cry (very loudly), they are also capable of various other functions, including... You know what, I'm not going there.
Otis in Milo And Otis is charged with caring for a chicken egg for a few hours and takes the role very seriously, watching the egg intently. It hatches on his watch and the new chick immediately assumes Otis is its mother.
Long before this trope developed, the C.M. Kornbluth story "The Education of Tigress McArdle" (1957), set Exty Years From Now, has a robot Toddler that works like this for adults as part of the Parental Qualifications Program which is actually a Yellow Peril plot; the Toddler is so obnoxious that it persuades a generation or two of Americans to get sterilized. The Chinese then move in to the aging and low-populated country.
Flour Babies is based entirely around this trope, as a boy looks after a bag of flour and discovers the truth about his parents.
Eve Bunting's Our Sixth Grade Sugar Babies, likewise, is a book whose plot is based solely on this trope.
In Holly Black's Valiant, Ruth and Val take care of a flour sack together, which prompts Jen to call them lesbians.
Unfortunately, Val commits infanticide so that she can use the flour to expose a faerie's glamoured apartment. When they fail the project, they try to scrape together a paper about the effects of post-partum depression.
In Lisi Harrisons The Clique, Claire's class takes care of synthetic babies; the data can later be uploaded to the teacher's computer.
In The Girl Talk series, they had an Egg-sitting episode, mostly for a "Not So Different" set up between Zek and a quiet pianist. Though it's notable for the fact the Alpha Bitch tried to cheat by boiling hers, and how a guy accidentally sat on his.
In Nothing But Trouble Trouble Trouble, the plot centers around the narrator and her friend being assigned to care for either a pet or an egg for the weekend and write it all down. First they try to kidnap a rich, bratty neighbor's two nasty cats, then are forced to return them and use the eggs. Then their eggs break, so they quickly purchase a mouse to use. And then that gets loose. All of this is kept secret, owing to the fact that the narrator's younger sister is very allergic to all pets.
Lifelike doll variant: In the Adrian Mole series, Adrian rents one of these dolls for his sister Rosie to help her decide whether to continue with her accidental pregnancy.
The point of Horton Hatches An Egg. A lazy bird doesn't want to spend her time sitting on her egg, so she cons Horton the elephant into doing it for her while she goofs off. Despite much teasing from his friends and being caught by hunters, Horton doesn't budge and eventually the egg hatches into a bird-elephant hybrid.
In Planet Tad, a regular feature in MAD, later released as a book, Tad and one of his classmates have to do this. So many of the kids in the class break their eggs that the teacher says that anyone whose egg remains intact will get an A for the project. Tad and his classmate nearly get one, until the teacher learns that Tad hardboiled the egg.
Buffy the Vampire Slayer, "Bad Eggs": Xander cheats by boiling his egg so it won't break. Lucky for him, because the eggs turn out to host demon parasites.
He was also going to eat his egg, before he learned it had a demon parasite in it.
Degrassi Junior High, "Eggbert": Spike and Shane are partners — appropriately enough, since he got her pregnant in a previous episode. The project helps bring out the worst in the entire cast.
Degrassi The Next Generation, "I Still Haven't Found What I'm Looking For": When Danny discovers that his sister is pregnant, he blackmails her boyfriend into helping him take care of the doll ("you need to learn this anyway"). It ends with the doll getting smashed in public.
Ned's Declassified School Survival Guide, "Bathrooms and Project Partners": Loomer steals the doll from Ned and Cookie, and threatens to send it back piece by piece if they don't do what he wants. Ned gleefully points out that they can just wait for Loomer to send all the pieces back, then put the doll together again. But their teacher moves the end of the project forward, before the doll's head is returned ....
Ned takes a "Life Science" Class meaning he and Cookie have to raise a doll the whole semester
On That '70s Show, Jackie uses this as a test for Kelso. The egg is broken and replaced, but he manages to explain away the missing pencil mark as having given it a bath.
Although this is usually played with high school age characters, (are) adult examples have popped up, usually among characters who doubt their abilities as parents (sometimes with good reason): Frasier used the trope in one episode, when Niles adopts a sack of flour to see if he is ready to become a dad. The humor comes in that the sack is singed, taped, glued, and otherwise maimed from a series of events that take place offscreen and are highly unlikely for babies to encounter (as Niles put it, "A real baby would have cried before bursting into flames."). Ultimately, the sack was chewed up by the dog and Niles treats the situation as if he had actually lost the child. He also had a dream where somebody kidnapped it and started sending him muffins in the mail.
Also used with adults on Las Vegas, where egg-sitting is a homework assignment for a couple's parenting class. The father-to-be's egg gets broken in his jacket pocket, while the expectant mother dresses hers up more like a pet chihuahua than a child. She also foists eggs off on other casino staff who aren't yet parents, so they can "share the life lesson".
Flash Forward: The main character, Tucker, has to take care of an electronic baby and babysit a live child at the same time. He manages to take care of the living kid, but the electronic baby is broken in an accident, which he tries to repair by using parts from movie monster kits that he collects.
8 Simple Rules used the 'Bag of flour' version: Everyone uses the flour for baking, leaving the "baby" deflated.
Hannah Montana: Oliver bonds with his partner while caring for a sack of flour and they start dating, only for him to discover they have nothing in common when the assignment is over.
Lucy and her boyfriend get this assignment on 7th Heaven. When something happens to their egg, Ruthie advises them to write that they aren't ready to be parents, which is the whole point of the assignment, anyway.
An episode of A Different World had this once, where one of the characters was obsessing over the egg as if it actually WAS her child.
Parodied, like every other high-school trope, on Strangers with Candy, where a teacher announces that "in order for you to learn what it's like to take care of a ten-pound 'baby,' each of you will be taking care of... a ten-pound baby." Sure enough, each pair of students is assigned a live child. Jerri and her friend Tammi quickly fall into the roles of "abusive husband" and "doormat housewife" repesctively, and the baby is spectacularly neglected in the process.
Castle: Alexis and her friend Paige do this with an egg ('Feggin'), asking Castle to egg-sit while she and the friend go to a party. Surprisingly, both Castle and Beckett manage to keep the egg safe. However, after Paige gets drunk at a party and Castle calls her parents, she "accidentally" destroys the egg.
Something similar in Sabrina the Teenage Witch. Instead of being parents, they simulated marriage. Libby naturally snaps Harvey up as her partner, and Sabrina is "stuck" with a nerdy guy.
On The Middle, Axel ends up dismantling the doll to get it to stop.
Veronica Mars has to "raise" a baby-like doll with her boyfriend Duncan for a sex-ed class. It's not clear if they fail or succeed, but Veronica definitely isn't shown to be a reliable parent. Also, the doll serves as Foreshadowing for the reveal that Duncan's ex-girlfriend is pregnant.
In one episode of Charmed, Paige rents a doll for expectant parents Piper and Leo to care for to see what it will be like to raise a child while constantly battling demons. Hilarity Ensues when the Demon of the Week shows up and the doll predictably doesn't survive in one piece.
How to Be Indie: The class gets an egg sitting assignment in "How to Get Gotten". Indie tries to dodge the assignement by volunteering to escort a seventh grader who is being trialed in the eighth grade for a week instead.
An adult example occurs in an episode of Kenny Vs Spenny. Each is given a lifelike doll that requires attention and records how observant the parent is. Kenny purposely mistreats and eventually “kills” his doll and then switches it with Spenny’s doll.
Everybody Hates Chris: Chris's class gets this assignment episode "Everybody Hates Eggs". Miss Morello being the naively racist teacher that she is, she gives Chris a brown egg and makes him do the project alone as a single father.
My Wife and Kids: Michael makes Junior take care of a water balloon to test if he is ready to be a parent. Junior draws a face on it and calls it Fetus Face. It is eventually destroyed when he slams down the hood of his car while arguing with Michael and the water balloon falls on the floor, followed by a montage of Junior and the water balloon together.
South Park, "Follow that Egg!": In order to spite her former lover, Mr. Slave, Ms. Garrison puts Stan and Kyle together for egg-sitting, expecting them to break their egg — and thus provide evidence against the legalization of gay marriage. When they don't break it, she hires a hit man to kill the egg.
Danny Phantom has Danny (secretly a half ghost) and Valerie, a fellow student, (secretly The Hunter, trying to capture Danny) take care of a microchipped sack of flour that can simulate crying and defecation. Tucker had the idea of "babysitting" other student's projects for money, but his mother used all the flour for cooking, forcing him to pay everyone back with interest.
Similarly, in O'Grady, Kevin (the High School Hustler and Humphrey) babysits everybody else's dolls for money. Abby discovers that he's been reprogramming the dolls' memory chips to record that everything is fine. She responds by reprogramming them to scream twenty-four hours a day.
Batman Beyond: In place of a real egg, Terry's Family Studies class uses a baby-sized artificial egg that's AI-enabled to cry, get "hungry" and generally respond like a real kid. Unable to get anyone to babysit his electronic egg, Terry has no choice but to take it along crime-fighting with him. Not only does Hilarity Ensue, he ends up getting the highest grade in the class, as only his egg was properly "stimulated" (it had the most fun). The Teacher says this is a sign that Terry is excellent father material, which pleases his girlfriend. (Notably, this is the episode of the series that won an Emmy, and the commentary on the DVD explains that they intentionally wrote a funny episode for their otherwise serious show as deliberate award bait.)
Also an interesting take happens with one couple:
Max: Here's the bio and civics.
Nelson: Thanks, hon. What about the math?
Max: It's coming, keep your shirt on.
Terry: I get it. You're doing his work for him so you don't have to take care of the baby.
Max: We opted for the traditional marriage: one breadwinner, one homemaker.
Nelson: Beats algebra.
Beavis And Butthead get a bag of sugar; by the end of the episode, it's in the teacher's gas tank.
A Kim Possible episode plays on this (and a really bad Meaningful Name joke/pun). Ron is entrusted with a sack of flour, which he's repeatedly forced to replace after a series of slapsticky mishaps. While he lavishes attention on "Sacky I" through "Sacky MCMXXXIIII", he ignores and deplores his new adopted baby sister Hana, whose name happens to mean "flower" in Japanese.
Hey Arnold!: Arnold and Helga get paired together and spend the entire assignment arguing, losing the egg in the process twice. The second time they find it, they put aside their differences to work together — and then the egg hatches into a baby chick.
The progress of the other students are also followed. Harold and Rhonda are paired together, for example, and she paints their egg to look like it has a baby's face and hair. She leaves to go shopping and Harold, who is apparently channeling Cronos at the time, gets very hungry and eats it. They ultimately turn in the egg shell, taped together.
Subverted on My Gym Partner's a Monkey - The students of Charles Darwin Middle School are given eggs to take care of. The eggs hatch into exotic bird chicks which must then be cared for.
Hercules The Animated Series has the students taking care of eggs as part of their project. Despite his clumsiness and tendency to trip over his own feet and cause chaos and destruction everywhere, Hercules kept his egg safe. Cassandra just went ahead and cooked and eat her egg in front of everyone else.
Carl Squared does it with sophisticated robot babies, including a microchip that records how well the students do at "parenting". Carl accidentally decapitates his.
Detention: The "babies" are water balloons, each of which has a device that cries at random and will lock into the 'on' position if the parent doesn't switch it off in time. The guys are either reckless with their babies or completely absent, so the girls add water to the balloons, saddling the guys with the extra-unwieldy babies. All the guys except Emmitt cause some accidental mayhem during a field trip, dropping their balloons in the process, so he and Shareena are the only ones that escape having to do the project again.
The Penguins of Madagascar had an episode where the gang found an egg and tried to care for it until it hatched. Only Private had any real sense of responsibility, putting the little thing in danger. Eventually, the baby was returned to its rightful mother.
An episode of American Dragon Jake Long had Jake trying to protect a griffin's egg from the Huntsman and Huntsgirl, with Fu Dog's help.
In the same episode, his class is given an egg-sitting assignment, which makes for a hilarious (But convenient) mix up.
Pepper Ann's class uses actual dolls as a way of teaching the students responsibility. After spending most of the episode failing at being responsible, she leaves a crying "Irma" on Nikki's doorstep. When she gets home, she monologues about how irresponsible she is as she turns off the lights and TV and prepares dinner for her sister. When her mother arrives home and comments on how responsible she is, Pepper Ann retrieves Irma (who stops crying).
Phineas and Ferb: In "Perry Lays an Egg", the boys find an egg (that they accidentally knocked out of a tree) that they believe to be Perry's. When Perry disappears, they decide to care for it... to the horror of Candace, whose maternal instincts have been awakened by a nature documentary. She tries to teach them the right way to care for an egg, which apparently involves dressing up in a platypus costume.
Kuzco on The Emperors New School has to do a class assignment with the others, each taking care of their own individual kitten. At his first attempt to care for it he throws it into his school locker (thinking it'll be fine on its own) and names it "Homework".
In one episode of The Simpsons, Bart gets himself emancipated and moves out due to Homer’s behavior. Homer does not take this well and tries to learn to be a better parent by caring for a bag of sugar. Somehow, the bag of sugar gets switched with a real baby.
D. W., the kid sister of Arthur on the PBS show Arthur, had a Tamagotchi-like (though on-line)"Net Kitten" that was imperiled when the family computer broke down. She asked her friend Emily to take care of it, then became jealous when Emily did a better job than she did.
In Life With Louie, Ora thinks she's pregnant and uses eggs to teach Louie and Tommy about babies. Since they think one of them will have to move out to make room for the new baby, they go to great lengths to prove who's more responsible.
A Canadian radio show once had the hosts adopt one of those lifelike electronic dolls when they were still brand new technology. "Baby Rocko" was dead within the week.
Supposedly, one out of each classroom set of the dolls is a "meth baby" which does not stop screaming. What purpose this serves, exactly, aside from being sadistic as all fuck, is a mystery, unless they think schoolchildren are capable of empathy (in which case they were never children).
Tamagotchi, simulated pets contained in egg-shaped digital devices, must be "cared for" by their owners periodically, making them a purely-recreational version of this trope.