How is crew resource management trained?
CRM training which I have been exposed to consists of lecture/videos to cover principles and expand on them with techniques.  There may be some classroom exercises.  However, due to the way that most training is conducted, the "classroom" is usually small numbers.  The application of CRM is in the simulator (SIM), where evaluation of techniques can be provided as the techniques are applied in routine and not-so-routine training scenarios.  Debrief is normally instructor(s) on team, after the SIM session(s).

For the training I get, CRM is pretty effectively integrated into recurrent SIM training.

For ab inito and primary training, the CRM training is similar, with classroom/video training.  Flight schools and academies will have larger class sizes and normally have quite a bit of depth in their training. I recently reviewed a 4 credit hour university course on CRM.

A friend who is a pilot, and also an Emergency Medicine Physician, (and with graduate and undergraduate degrees in Human Factors and Industrial Engineering) has been applying CRM to the hospital emergency department operations, and the military has similar efforts.

CRM has been around for a long time, although there were cultural impediments to it's widespread integration in the aviation context.  Much of that continues to change over the last 20 years.  I expect that CRM will expand into areas such as varying personality styles and other team techniques in the future. An example is some of the people style recognition and skills as developed by Robert Bolton, PhD and Dorthy Grover Bolton.

To summarize, the method of teaching is dependent upon the venue.  In many areas of aviation, CRM is integrated into recurrent training and critiqued on observed operations.  In initial training, the introduction of CRM is largely dependent upon the style of instruction, and whether that instruction is individualized or team based.