Informal words in essay

[Hannah's fan]

As a teacher, do you encourage using informal words in student's essays ?

will the essay full of informal words score high mark in the exam ?

thanks for ravelling out this long-haunting question.

 

[Raymott]

As a teacher, do you encourage using informal words in student's essays ?
No.
will the essay full of informal words score high mark in the exam ?
No.
thanks for ravelling out this long-haunting question.

Students can generally pick up informal language easily if they know enough formal language. It's OK to use informal language if you're writing dialogue (and advanced skill) or if, for some reason, the teacher asks for an informal essay.
One reason for this is that informal language is generally unstable. It comes and goes over time; and it's not likely to be as universal or useful as formal language.