In (proper!) UK English, it's written with a hyphen. I don't know about US English or other variations of English. If you Google it, you'll find all three forms widely used!
Extracurricular is one word.
1
The word extracurricular comes from the two words " extra & credit ". So since there is only one ful word that is in the word " extracurricular " extra is the root word.
"After school" is typically written as two words.
Contracted words.
Chess player is written as two words.
"Pogostick" is typically written as one word.
"all day" is typically written as two separate words.
Hard work is written as two separate words.
Two words.. one hundred.
"Fact sheet" is typically written as two words.
"Crash site" is typically written as two words.