My favorite book on the Early Church Fathers comes from Mike Aquilina. Mike's done us all a wonderful favor and greatly expanded The Fathers of the Church. It'll be available for purchase in September. If you're planning the school year for your bright high school child, I would say that this is essential reading. (It's often used as a textbook in universities.) For more detailed information about the additions to the book, go to Mike's blog. To order it, call OSV at 1-800-348-2440 and make sure to tell them that you want the new, expanded version.
PS to my sister. This would be a great gift for a pastor husband!