There is only a silver MacBook Pro. Apple advertises the 15.4" model as having up to 6 hours of battery life. In practice, usage time may vary based on display brightness, processing activity, and use of connectivity options i.e. WiFi and Bluetooth.
If it's a new computer, it should be lasting longer than two hours on a full charge provided the display brightness is kept low. What do you need a laptop for in class, anyways? You should be able to use your MacBook Pro for word processing for over three hours on a full charge.