Offering training programs is something that most certifying agencies consider taboo. If the subject comes up among a group of certification professionals, within a split second the rationales are flying:
It's a conflict of interest. It's against NCCA standards. That's the association's purview. Matter of fact, I found the following training policy on the web (organization name removed to protect the "innocent").
"Because of its third-party status as an independent provider of certification, the ___ is unable to offer training. Third-party providers of services are generally prohibited from offering any related service because of a potential conflict of interest in the outcome of the certification process.
Offering both training and certification is also expressly against the rules of professional certification as laid down by the National Organization for Competency Assurance (NOCA) and the National Commission for Certifying Agencies (NCCA). ___is an NCCA-accredited organization
Nevertheless, ___ considers training to be vital to the certification process. Indeed, one of its principal aims has been to stimulate the recognition for the need for professional instruction in the knowledge and skills that define ___ competency."
It is not In violation of NCCA standards to provide training programs (or even prep courses) related to certification programs. Providing them is not the problem. REQUIRING THEM is a problem (can you say, tying arrangement? - as in tying the certification product to the training product). Stating or implying that the training is the only available route to certification is also a problem. (See NCCA Standard 2 Commentary D.)
Let's think logically. Who other than the organization that identified the body of knowledge would be most qualified to create training based upon it? Isn't it supportive of your mission to support/improve the competency of professionals in the field?
Of course, you need to approach training development and delivery responsibly. Individuals directly involved with certification test item writing should not be involved in course development or delivery. If you are part of a membership association or have a relationship with one that already has this type of training, you should be respectful of that, and work with them to see what configuration makes sense (ideally, you'll find an appropriate role for both parties). You'll need to be very careful in your promotions of the training. Again, do NOT require it or state/imply it is the only route to certification available. And, don't make any promises about the link between taking the training and passing the certification test. Matter of fact, having disclaimers regarding that is a great idea.
In the end, you may decide that training isn't something your organization should or could do, and that's okay. My aim is not to convince you that you should. It is not always appropriate, strategic, and/or profitable. But, let's be clear, certifying agencies CAN offer training.