Motor Shield StepMotor
There are two types of stepper motors: unipolar and bipolar. Bipolars usually have four wires and unipolars have six.


  
  
  --http://hobbymilling.com/wp-content/uploads/2011/05/Unipolar-stepper-motor-windings.png
  
  
  
  --https://www.codeproject.com/KB/system/steppermotorcontrol/pic6.jpg


The motor shield is designed to drive a bipolar motor (4 wires) but the motor is unipolar (6 wires). As you can see in the pictures, if you ignore the middle wire of the unipolar motor, it is the exact same as a bipolar stepper motor.