Samuel Martin, Religious and Hebrew Scholar, has written a book about Christians and the Spanking Controversy. You can also have him email you a free PDF file of the book by sending a request to email@example.com or download it here. More about Samuel Martin and his book(s) here.
NoSpank has a PDF book on their site called, Nonviolent Christian Parent.
If you must read “To Train Up A Child” for research and don’t want to buy the book, you can read it here.