Fabulous premise. British boarding school? Yes ma'am. And dark academia, nonetheless. I haven't found many (by which I mean only one other) middle grade books with this setting/vibe. Then there's the searching-for-my-lost-dad trope, and the diverse characters, although they weren't as 3D as I hoped they would be.
But the execution... eh, could've been better. I kept rewriting things in my head. I had to suspend my disbelief more often than I would've liked. I don't mind unrealistic elements in a book that's supposed to be unrealistic, but this felt like the author was taking liberties because she thought her audience would be too young to care.
So, the story was great. I ate it up, and I'm planning on reading the rest of the series, too (mainly for the Latin Society and Jack). But if prose and voice are important to you, this might not be the best use of your time.

PS: Ooh, but extra points for the cover art. It's so perfect. I want the whole series just so I can look at them on my shelves.