Ooh, a chance to be technical. I love getting technical about these sorts of questions.
So, most style guides have a specific guideline for numbers, and it varies by field (fiction versus journalism versus scientific writing), and by region, and by tradition. Oxford University Press’s house style guide says certain fields (law, social sciences, and humanities, if I recall), spell out numbers ninety-nine and below, and use figures from 100 onwards. For fiction, ten is spelled, 11 is written with numerals.
Then, The Chicago Manual of Style has numbers up to 100 spelled out OR numbers up to 10, publisher’s choice, and numbers ninety-nine (or nine) and below written, with exceptions for situations like “They donated 102 buttons and seventy-six spools of thread” where one can choose to write out or use numerals for both, for consistency’s sake.
And I’m sure there are exceptions, but every English-language style guide I’ve used has hyphens only used between twenty-six, thirty-one, and the like, and no-where else within spelling out numbers. (Maybe that’s why some style guides allow for numbers spelled out up to ninety-nine; where we would get to use the hyphenation rule if we stopped at ten or twelve?)
There is even a certain amount of logic for the use of ten, twelve, and one hundred as the cap for when to switch to numerals. The thinking with choosing one hundred as a cap has to do with saving space and our using a decimal numeric system. “The log split in two” does often seem more organic, but “there were 1,265,978 grains of wheat in the sack” is much better than “there were one million, two hundred sixty-five thousand, nine hundred seventy-eight grains of wheat”. That’s also the logic behind spelling ‘a million’; it’s shorter than writing out 1,000,000 and may be easier on the reader’s eyes.
The traditional logic for spelling out numbers up to ten is a bit odder, so I thought it deserved a mention. A lot of systems in the English language for dealing with numerals have to do with a long-running idea that ten (or sometimes twelve) felt ‘natural’ to early man. Ten fingers, or sometimes one sees quantities of twelve if one counts both hands and thus progresses a bit further. (Some people also use this explanation to explain why we have a specific word for ‘one dozen’, but I’m not sure how legitimate that explanation is and I’ve never researched it myself.)
Since even ancient Babylonians used something very much like early modern calculus equations to calculate their star charts, this ‘ten fingers’ explanation doesn’t necessarily convince me. Mesopotamians used base sixty and very seldom wrote out names of numbers rather than using digits…But still, that ten/twelve threshold affects a lot of modern thinking about numbers and their integration into daily life.
I’m a bit surprised to hear this. The universities that I’m familiar with all have a style guide assigned to various departments, and grading on grammar has more to do with how well one conforms to the style guide, not how whimsical one’s teacher is feeling about Oxford commas. And of course you can then petition if you’ve received poor marks due to grammar but you’ve been following the style guide correctly. Another reason why style guides are useful!