Background Paragraph: Acceleration is a measure of the change in velocity of a moving object. It measures the rate at which velocity changes. Velocity, in turn, is a measure of the speed and direction of motion, so a change in velocity may reflect a change in speed, a change in direction, or both. Both velocity and acceleration are vectors. A vector is any measurement that has both size and direction. People commonly think of acceleration as in increase in speed, but a decrease in speed is also acceleration. In this case, acceleration is negative and called deceleration. A change in direction without a change in speed is acceleration as well. 
Story: Johnny is playing with a toy train set his parents bought him. The controls for this train set allow him to make it go faster or slower and it even has a rail switch to make it travel on different tracks branching off to the left or right.
Given Johnny decides to make the train accelerate and change tracks, will the velocity of the train increase or decrease? Given Johnny decides to slow the train down, will this be an example of acceleration or deceleration? Will Johnny using the rail switch be an example of a change in direction or a change in speed? Will making the train switch to a different track be considered acceleration, yes or no.?