Is there a source anywhere (either online or printed) where I could find out exactly what each of the exercises in the Dozen A Day series of books is for?

I doubt it. The exercises in each book are for a wide variety of different things, so you'd probably need to look at the books themselves to get an idea of what they cover.

I've got all the books but there are no descriptions inside to say what each exercise is for. Having been taught some of them you wouldn't know just by looking at the book what you're supposed to be learning.

Just wondered if there was something else that explained the exercises and what they are trying to achieve as the explanations are missing from the books themselves.

There is no "explanation" of what each exercise is trying to achieve, but by looking at each one, teachers should be able to tell. Even though sometimes my students will say "Oh this is easy" - I will make them look "beyond" the notes on the page and make sure that the technique of the hands/fingers/arms, etc is correct. It's easier to correct and focus on technique when the pieces are "easy". Other times I have the students try to discover what the exercise is trying to achieve. We discuss this together and how it helps them as they are reading and practicing their literature pieces. As the books get harder, we discuss how the concept was presented in past books and how it is being extended and developed now.

I'm wondering how you teachers feel about assigning these dozen a days to your adult students. My teacher was almost embarassed to ask me to do these at first, I guess because of the silly stick figures on the pages. I'm glad she did, however, and after seven months can't imagine starting my day without them. They are very good about exposing little weaknesses and I really like the way the exercises build up each other.

My adult student loves Dozen a Day. I think when she is struggling with her pieces week after week, it's nice to have a little nugget she can master.

Dozen a Day is a great series and it is nice that they are so short and you can introduce your students to the metranome with them. For my beginning students when they pass one I let them put different colored happy face stickers where the head is supposed to be, they love it. But I don't hesitate to give them to my adult students also, Dozen a Day that is not the happy face stickers. Finger Power by Schuam is another great series and I often intertwine the two.

So I guess they are not really suitable for students who are self teaching as the exercises have no explanations?

Not really. For that, I'd recommend the technique books from Catherine Rollin's Pathways to Artistry series. They include a fair amount of explanation.

I just started using this series, and I like it very much.