A young homeless girl, Wise Child, is sent to live with the local wise woman, Juniper, in a place that might be Scotland, and at a time that might be the Middle Ages... Wise Child learns Latin, mathematics, herbal and healing lore, and a bit about the making of magic.
If this book sounds interesting, there are two that follow: Juniper and Colman (Wise Child is my favourite). I found them in the 'teen' section written by Monica Furlong.