As with other artistic professions that we have covered in this growing series of articles, the training needed to work as a print designer varies from project to project, from company to company, and artist to artist. Most of the people I talk to have some formal training under their domain, often in graphic design or illustration. While certification may not be necessary (although most of what I have spoken has had a relevant BFA forum), designers have to build their portfolio to get this job regardless of whether they work at home or on a freelance basis.
Formal education allows designers to hone their skills, learn about various print design projects, and build their portfolio by interacting with students and other professors. Also, ideas, projects, and techniques that may not have happened to the student may be assigned. Having the opportunity to try and fail things before starting the right work is a great experience for artists everywhere, yet they can find it.
Knowing the ins and outs of design software such as Adobe InDesign and QuarkXPress is often necessary for CVs (along with editing and moving various digital designs) as most, if not all, the design is digitally created or assembled these days. Digital art classes often help with learning about such programs, although they are also quite situational. The point is not how you master your profession and the tools to create it, but what you learn.