From 1929 to 1972, Dr. Cornelius Van Til was professor of apologetics at Westminster Theological Seminary, Philadelphia, and then professor emeritus at Westminster until his death in 1987.
In letter #2 of Schaeffer's posthumous book The Letters of Francis A. Schaeffer, he writes
The three and a half years since I came to Europe have been the most profitable in my life, with only one possible competitor, my three years in seminary.It is not commonly known that Schaeffer attended Westminster Theological Seminary. There, he was a student of Dr. Van Til, and was taught presuppositional apologetics. Thus, it is no coincidence that Schaeffer's first book, The God Who Is There, should feature a lengthy section on presuppositional apologetics.
In order to properly understand Schaeffer's apologetics, it would serve us to understand the man Schaeffer learned apologetics from.
Francis A. Schaeffer ping!
Based on Van Til's letter, it appears that Schaeffer didn't always agree with van Til.
If you Google Cornelius Van Til you can find an article on "Why I believe in God". This one of the best evangelistic and teaching tools I have found and used it as the basis for a four week Bible study. He along with Machen were heroes of the faith during the modernist wars.
Van Til Bump!