Granovetter's "strength of weak ties" hypothesizes that isolated social ties offer limited access to external prospects, while heterogeneous social ties diversify one's opportunities. We analyze the most complete record of college student interactions to date (approximately 80,000 interactions by 290 students -- 16 times more interactions with almost 3 times more students than previous studies on educational networks) and compare the social interaction data with the academic scores of the students. Our first finding is that social diversity is negatively correlated with performance. This is explained by our second finding: highly performing students interact in groups of similarly performing peers. This effect is stronger the higher the student performance is. Indeed, low performance students tend to initiate many transient interactions independently of the performance of their target. In other words, low performing students act disassortatively with respect to their social network, whereas high scoring students act assortatively. Our data also reveals that highly performing students establish persistent interactions before mid and low performing ones and that they use more structured and longer cascades of information from which low performing students are excluded.