Sit in the back of the classroom where you will create a minimum amount of distraction for the trainer.
Take careful notes regarding the performance of the trainer. Measure the trainer's speaking speed, comfort in front of a group, and how easy he is to follow.
Make a note of any areas of the class that seem unclear or rushed. Students should leave internal training courses with a new skill or broader knowledge.
Participate in all class activities. Engaging in the group classroom activities gives you hands-on experience and subjects you to the experiences of trainees.
Sit down with your training staff to talk about classroom shortcomings and how they may be improved.