This is the 5372nd most frequent Korean word.
뒤에도
"뒤에도" means "even behind" or "also behind" in English.
In this sentence, '뒤에도' is used to indicate that there is a park situated behind the school in addition to another relevant location.
나는 학교 뒤에도 공원이 있는 것을 발견했다.
I discovered that there is also a park behind the school.
Here, '뒤에도' refers to the time after the class, implying continuation beyond the class period.
수업 뒤에도 추가 공부가 필요하다고 느꼈습니다.
I felt that additional studying was necessary even after the class.
'뒤에도' in this case is used spatially to denote the presence of people further back in the line beyond the friends.