Kids at Argonne Elementary in San Francisco dressed up as idioms, the expressions that can't and should not be taken literally.
"I'm dark as night," said one student.
"I'm a piece of cake, but a whole cake because it makes it even better," another student said.
There were lots of others: driving me nuts, out of the frying pan and into the fire, raining cats and dogs.
"I'm all ears," another student said.
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"It helps kids think about the language. It especially helps our language learners, our kids for whom English is not their first language," said teacher David Allyn.
Another school, San Francisco Montessori, made it a historical Halloween. Third grade students spent a month researching a famous person and were asked to get into character. Among the greats were Jackie Robinson, Walt Disney, Albert Einstein and Ruth Bader Gingsburg.
"It keeps them to continue learning and Halloween becomes continued education," said Lindsey Keener, a teacher.
Students at Bryant Elementary in the Mission District were asked to not judge a book by its cover, read it instead and dress up as one of the characters. There were many sinister characters, like the "deadly bride."
"Years passed and no one would find her and she died," said the student who dressed as the deadly bride.
Non-fiction books were also welcomed, like "The History of Football."
"It helped me read more because I thought if I am reading a book that I know about, it will help me get more information on it," said Marquise Diaz, who dressed up as Vernon Davis.
And most there did everything by the book.