The Incandescent, by Emily Tesh

Dr Walden is director of magic at Chetwood School, a cross between Rowling's Hogwarts and Novik's Scholomance, where she is charged with keeping students safe from ravening demons who would like to feast on their burgeoning abilities. When ambitious A-level students summon a demon beyond their powers to contain, Walden has to draw on everything she has to save them and protect the school. Unfortunately this drags up demons from her own past at the school, putting herself and everything she cares about at risk. After a slow and heavily expository beginning this tale develops into an interesting psychological examination of magical teachers and students, with an appropriate British touch of class, wealth and status. The characters and their relationships are well developed and credible. The ending is a little pat, but offers some optimism and the possibility of redemption with a possible sequel.