How important is school? Well, for you soon-to-be graduates, that's a question you may think is far too late to ask. But before you throw your hands up in despair, know this; when it comes to higher education (or any level of training, for that matter) you get out what you put into it. So if you put forth a concerted effort towards your classes and your projects, breathe a sigh of relief. Of course, if you coasted through those classes, never truly applying what was being taught, you may want to take a moment to evaluate yourself and your work.
People are different and learn differently, everybody knows that, and employers and recruiters are not likely to ask or care about your Grade Point Average. They want to see your work. This is especially true in creative jobs. So maybe you don't do well in the traditional classroom environment. While your grades may not demonstrate it, you may be the type to constantly strive to learn and do better. This could very well show through in your portfolio. On the other hand, you may have received good grades, but only did what was expected and nothing more. Maybe you put forth the minimal effort or worked with teams who made you look good by proxy. This too can be surprisingly easy for potential employers to catch.
Jobs in the creative field (and especially advertising) are difficult to come by. If that's what you truly want to do with your life, put forth the effort to truly learn your trade, not to get good grades, but to do exceptional work.