If you are teaching through the Westminster Shorter Catechism, make sure to check out this commentary by A. A. Hodge and J. Aspinwall Hodge - The System of Theology Contained in the Westminster Shorter Catechism: Opened and Explained (1888). A. A. Hodge had written the first part of the book, and upon his death J. Aspinwall Hodge (his cousin) finished it. This relatively unknown volume is a great companion to Hodge's Commentary on the Westminster Confession.