When test driving a new car or when borrowing a friend's car, people successfully navigate the process required to find the ignition switch, to work the clutch and the manual transmission, to locate the turn signal switch, and to operate the radio and CD player. The process may not be flawless, but the experience of having driven numerous cars in the past provides a variety of learning trials for successfully operating ignition switches, clutches, manual transmissions, turn signals, radios, and CD players. Similarly, when students learn to add and subtract numbers with objects and on worksheets in the classroom, we expect them to make change accurately when purchasing items in their community stores or successfully manage time-telling tasks that require adding or subtracting minutes. ...