I'm in a Master's Program for Clinical Psych. I had a pretty good GPA (3.7ish), but people in the same program have stuff like a 3.3. If on some off chance you have a publication already or even a poster, that's pretty much an automatic acceptance at some places. Letters are probably most important after that, then probably GREs or your personal statement/interview. GPA kind of weighs little due to the fact that it's too variable. You could take the minimum for your major and a bunch of easy buffer classes and end up with a higher GPA than someone who actually cared to learn useful stuff, but got more Bs.
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