The structure of executive functions or frontal-lobe functions remains an active debate (see Miyake et al., 2000). Whether executive functions are considered separate abilities or a unified ability, planning ability is consistently included among the ranks of executive functions. A common variety of tasks used to assess planning are tower-transform problem-solving tasks. The classic tower-transform task is the Tower of Hanoi (TOH), but a towertransform task that is gaining prominence both in clinical and research settings is the Tower of London (TOL; Berg & Byrd, 2002). The objective of the TOL is to rearrange a set of three differently colored balls or beads placed on three pegs of the game board to exactly match the balls in color and position on a separate goal board (see Figure 13.1). The balls may only be moved one at a time from one peg to another, and the length of the three pegs is designed to hold only 3, 2, or 1 ball, respectively. With different arrangements of game and goal balls, problems may vary in difficulty, with optimal solutions requiring from 1 to 8 moves.