I read this book because of the cure song "Charlotte Sometimes" during my teenage years. It was a little past my age reading group but I was never the sort to care about age labels on books.
That said, I did find it difficult to get into "The Summer birds" because it was too childish at my age now.
Charlotte is transported to WWI era England every other night from her magical bed. The book is about her adventures and the relationship she ends up sort of having with the girl whose place she took.
I learned about all the British boardingschool terms like prefect before Harry Potter from this book.
I loved the character Bunty the best. Bunty would be excited about the small things like having currants in her buns. That is oddly enough one of the details about the book to stick in my mind. I found the war ration stories interesting sort of like the sugar shortages in Gravity's Rainbow from Thomas Pynchon.