The International Association of Chiefs of Police website lists the process for certification for DRE training. Everyone who's involved in the program has to first take the standardized field sobriety training before they attend the DRE program. Then the program itself consists of three phases. The first phase is a two-day preschool. The second phase is a seven-day classroom program with a comprehensive exam following that. Then between 60 and 90 days following phase two, the candidates attend a program in the U.S. where they have to evaluate subjects who are suspected of being impaired by drugs. My understanding is that they must participate in at least 12 evaluations successfully in order to then get the certification.
On September 12th, 2017. See this statement in context.