fail in (something)
1. To not have high enough grades to pass a particular class. My parents got my report card and grounded me because I'm failing in two classes.
2. To not award a student a passing grade in a particular class. In this usage, a noun or pronoun can be used between "fail" and "in." I failed you in biology because you missed so many classes this semester.
3. To not be successful in an attempt to do something. So far, I've failed in my efforts to find an internship for the summer.
fail in something
to have not earned passing or satisfactory grades in some school subject. George is failing in geometry. I hope I do not fail in math.
1. To fail to achieve some goal or effort: I am failing in all of my attempts to win the contest.
2. To achieve unsatisfactory grades in an academic subject: Because I am failing in math, I am seeing a tutor.
3. To give someone an unsatisfactory grade in an academic subject: My teacher failed me in algebra despite my hard work.