Here's why:

* Magnitude: Acceleration has a magnitude, which is the rate of change of velocity. This tells us how much the velocity is changing.

* Direction: Acceleration also has a direction. It tells us the direction in which the velocity is changing.

For example, if a car is speeding up, its acceleration is in the same direction as its velocity. If the car is slowing down, its acceleration is in the opposite direction of its velocity.

Since acceleration has both magnitude and direction, it's classified as a vector quantity.