If I hadn't read Grave Mercy by Robin LaFevers first, I might have rated this one a tad higher. Ditto if the book hadn't been clearly stated to be written for ages 13-17.
According to the author this series looks at historical what ifs: what if King Louis XVIII had been assassinated? In this historical context she creates a school for girls with unusual...talents. A School for Unusual Girls focuses on Miss Georgianna Fitzwilliam (no way Baldwin isn't a P&P fan), a 16 year old with a brilliant mind for mathematics and science. Abandoned at Miss Stranje's school because she set her father's stables on fire in the midst of an experiment, she's intent on escape until she is offered the chance to perfect her formula for invisible ink.
The story is great and the characters are finely crafted but the writing lacks the subtly of LaFevers Grave Mercy or even Ransom's Miss Peregrine's School for Peculiar Children, both of which follow the same basic premise. Baldwin does not want her readers to miss a moment of Georgianna's angst, denial and sense of abandonment by her family, so she rather bashes the point home for the first third of the book. I almost didn't make it past the second chapter as her desperation became rather too thick.
Things picked up a bit after page 85, although it was replaced with romantic longing; this was done, thank goodness, with a deft hand, which helped to soften the effect of our MC being a wounded puppy. The suspenseful tone of the rest of the book kept me reading. I liked it in spite of the MC, and because of the rest of the cast of characters (and a truly evil villainess with all the best lines). It was a great way to lose myself in a lazy afternoon when it's too hot outside to do anything else.
There's apparently at least a book two from the POV of one of the other characters. It's one of those that I'd definitely pick up if I ran across it, but it's likely not going on any "must" lists.