I tried to add that but the edit function already locked me out. Here’s about what I was trying to add.
I would say the Mesopotamian use of clay tablets was possibly the first use. After all wet clay is rather easy to chew up until dry. I don’t think a hard clay tablet would stop them, as I see dogs insist on chewing stones all the time.
I can tell you it wasn’t used in Spain until pretty recently, and I reckon as an influence of English-language media. So my first question would be, which cultures use it?
I don’t know if I qualify as an “older Doper” (I hope not), but when I was in eighth grade my dog really and truly did eat my English homework. I was worried that my teacher wouldn’t believe me, so my mom sent me to school with a note for my teacher that said something like “Dear Mr. Guernon: Please excuse skammer for not having his homework today; he did the exercises but his paper was destroyed by our puppy. Really.”
Signed,
Epstein’s Mother
rofl! 
I do recall someone in my seventh grade science class saying the dog chewed up her homework.
Don’t remember if the teacher bought it, though.
Thank you, one and all! I hate that I don’t know how to search for stuff that would have given me the answer I was looking for, but I love that you all are so willing to do some of the work for me! 
In all seriousness I think that the cliché mainly arose from the fact that dogs, especially untrained puppies, have an amazing capacity to kill the living shit out of scary looking inanimate objects that are left on say, kitchen surfaces, and homework tends to be exactly the the kind of fauna that lives in that environment.
When our dogs were puppies they notched up an impressive loose item body count, and whilst none of it was technically homework, they did destroy one of my exercise books, and the teacher was dubious even when presented with the wreckage (I mean seriously, did he think I’d gnawed it to pieces myself? :rolleyes:)
I had a calculator (assigned to me by the school for one of my classes, IIRC) get chewed on by our dog. One of those indestructible blue Texas Instruments calculators with the case that slid on and off. Definite chew marks all over it, but it still worked fine, so the teacher decided she wasn’t concerned about it.
Cooking school?
“The Dog Ate My Homework”
“Don’t be ridiculous. Dogs won’t eat homework.”
“They will if you put peanut butter on it.”
Of course, a few years ago computer science students could reasonably claim that the DOS ate their homework.
You think it’s embarrassing to tell the teacher your dog ate your homework?
My mom’s a sixth grade teacher. She has a dachshund. Bad combination. Try telling 30 twelve year olds that your dog ate *their *homework! Yes, it’s really happened, although only once or twice in many years of teaching.
I’m another 1960s student who clearly remembers the excuse. No one actually used it; the teachers just gave warning they wouldn’t believe it.
I flunked my animal nutrition class because the dog wouldn’t eat my homework.
Actually, there are various myths about St Kieran (or Ciaran) involving foxes (and wolves, and cows, and badgers, and stags… The Irish really had a thing for Saints and animal stories.)
The one closest to “a dog eat my homework” would be:
This is riffed on in other versions of the legend, such as
There are more versions to be found online. There is no clear consensus on the date of his birth or death, so I’ll arbitrarily pick 516-549 from one of the websites quoted. I’m too lazy to look up the standard rate of graduation for Irish monks of those times - if it was anything like some of the Buddhist monks of legend, he might well be described a “student” at the age of 50. (You know, if he’d ever got that old.) Let’s say, arbitrarily, thirteen, although I gather noblemen might send kids to a convent for an education from age eight.
If we assume this story to be contemporary, and for a rather loose definition of “dog” (it was a fox) and “ate my homework” (in one story he eats the satchel, in another he explicitly doesn’t get to eat the homework) we could make a case for the story to have appeared maybe as early as, say, 529. This conclusively proves that this excuse can be dated back at least 1482 years.
Assuming the Catholic church hadn’t assimilated it from earlier folk stories.
It was a kid who did a science project on mammalian milk production stated that his dog has eight tits.
A bigger problem I see with all this early dating is the concept of homework. How long has that existed as a separate concept?
I woudl think that since people often walked far to a teacher, and had agricultural chores during certain parts of the year, that homework woudl have been more the norm and that classwork would be the newer concept.
This did actually happen to my sister. She made a model of something or other out of Play-Dough, and the dog ate most of it. My mother had to send a note to school confirming that it really happened that way.
The public school is by far the more modern concept.
Schools throughout most of history were for a few privileged children (almost always male) of the rich. Even to call them schools probably exaggerates it. They would have private tutors who lived in the household as a minor member. A few tutors became famous enough to draw students, but these would still be the tiniest minority of the rich.
When schools of a more recognizable sort developed (often church schools in the West) pupils boarded there, sometimes staying for years without ever returning home. Students got exercises to do outside of classes, mostly reading, but homework as we know it wouldn’t have been likely. That had to wait until paper got so cheap and ubiquitous that an ordinary family would have enough of it to waste.
Public school systems were in place in most American cities by the mid-19th century but U.S. students then did their schoolwork with chalk on slates, so that they could be erased and reused all year.
I’d be surprised if assigned homework that would be expected to be done on paper and returned the next day was common in any American school until the 20th century. (Maybe late 19th for a few places in a few large cities.) And I’d be more surprised if its use in urban schools didn’t precede its use in rural schools by 20 years or more.