A program is a plan, schedule or procedure to be followed to a specified end. An OG program follows a set scope and sequence.
An approach is the means adapted to tackling an issue. Orton-Gillingham is an instructional approach. It is most properly understood and practiced as an approach, not a method, program, system or technique. In the hands of a well-trained and experienced instructor, it is a powerful tool of exceptional breadth, depth, and flexibility.