I learned so much about R on the job, even after only taking one dedicated R course. The working environment with fellow students also makes the job much more meaningful and my interactions with the professors was smooth and always interesting.
What I wish was different
I wish the student team had more autonomy regarding its contributions (i.e. given more opportunities to substantively offer creative solutions and suggestions. Certainly, it's important to remember that our positions are as interns, but many times it felt like we were assigned the busy work, which is not unimportant but I just wish comprised less of my summer.
Be proactive with both the other student fellows and the professors--they're all such valuable resources.