I would recommend this drama to young children up to high-schoolers. It's overall a really light watch, that doesn't require heavy thinking and is aimed at younger audiences.

Although the plot is kind of ridiculous, the actors themselves are actually good.

I mean, even with the schooling system in South Korea, there's no way the students, parents, teachers, news reporters and the whole country would stay quiet if so many students of the same school killed themselves one by one, no matter if they were all bottom of the school when did it. No parent would sent their kid to such a school, no matter how prestigious it was. This would quickly come to the attention of the public. Plus there's no way the police wouldn't find anything suspicious after the 3rd consecutive "suicide", not to mention the following ones. And before they'd even start to investigate things, they'd first shut the school down.
A few more unresolved/open to question aspects are that 1. the mother of the female lead didn't even come help in the final showdown when her daughter could've died for the sake of the drama plot and 2. we didn't find the original story of the evil spirit. It was hinted that he was maybe a teacher who was obsessed with getting rid of the bad students, but would've been curious to find out more abt him.

Anyway the main leads were really cute. I especially followed Nam Da Reum after he played the child version of the main lead in While You Were Sleeping, and tried this drama because of him.
I only finished the drama, despite how childish it was, because all the actors, main or supporting, were actually good. Plus the episodes were short and I watched them in double speed lol.

Random p.s.: I have to say this short hair doesn't suit Kim Sae Ron at all.