I really couldn't bare this drama through to the end, however I know some people that did, so I recommend Angel's Last Mission to anyone that enjoys plots similar to this one.
Both dramas feature L as a main lead and personally I enjoyed the latter as there was a much stronger plot complimented by the comedic arrogant female lead :)

both dramas are similar in a way that the plot surrounds students being pushed to do extreme things in order to pursue a successful future.
however, sky castle focuses a lot on family reputation and how one failure in the family can drag everyone down altogether, leading to a lot of mind manipulation and emotional casualties.
definitely recommend watching sky castle if you enjoyed extracurricular!