<em>Not bad- I understood everything! I'd probably phrase it more like:</em>

The most important people in Korea's hagwons are not the students, but the parents. Because of this, instead of effective teaching methods, methods that the parents like are used.

<em>Also,"therefore" can be used, but because of how the sentences are structured, "because of this" comes more naturally to a native speaker. </em>

Haha the comments above are so funny. I was like what??? but I guess you miscategorized.

Anyways, see my comments below:

Practicing "효과적이다" with some miscellaneous grammar mixed in

한국의 학원들에서 제일 중요한 사람들은 학생이 아니에요. 부모님들 이에요. (I stongly agree!!)

그러니까 효과적으로 언어 가르치는 기법 대신 부모님들이 좋아하는 기법들은 사용해요.

The most important people in Korea's hagwons are not the students. They are the parents. Because of this (therefore?), instead of effective teaching methods, methods that the parents like are used.

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I'm sure there's a lot that's wrong with the above statement, but is it understandable?

미리 고맙습니다 (<-- I'm trying to say "thanks in advance") You could say this or you could just say "고맙습니다" only.

I was born and raised in Korea and I know exactly what you mean. 

I feel sorry for the students.