Barton was #32 out of 100 on "Baseball America's" Top 100 Prospects list in 2005. After having an emergency appendectomy part way through spring training, Barton started the 2005 season slowly, but ended the year with a .317 batting average. He spent most of 2005 with the Single-A Stockton Ports of the California League, but also appeared in 56 games for the Double-A Midland RockHounds of the Texas League. He was also selected to play in the All-Star Futures Game at PNC Park in Pittsburgh. With the Cardinals, Barton played catcher, but the Athletics moved Barton to first base due to concerns with Barton's ability behind the plate, the negative impact catching can have on the development of a young hitter, and because the Athletics had a number of more advanced catching prospects (Kurt Suzuki, Jeremy Brown, and Landon Powell).