<p>This study offers a methodological contribution to Mixed Methods Research showing how the temporal complementarity of data collection methods may be particularly suited to analyze medium-term social processes using a qualitative-driven mixed-methods approach. The temporal triangulation of qualitative and quantitative data enables a dynamic understanding of how social ties evolve, by capturing their transformations across time, space, and individuals. Beginning data collection by ethnographic observations, then administrate survey and finishing by interviews within a couple of months helps to understand a single phenomenon with various timepoints. This article illustrates how the different temporalities covered by data collection methods are complementary when addressing medium-term processes. To picture the relevance of this methodological framework, we rely on a study of bullying in four French middle schools, focusing on the early stages that lead to repetitive aggression between pupils. This empirical case highlights how sociability and aggression ties coexist and interact in the formation of bullying relationships. One type of relational dynamic emerged and is described, the failed friend case, where friends turn from playful to harmful aggression. This exploratory finding emerges from the use of temporal complementarity in data collection methods which enables a better understanding of how relational histories shape current behavior.</p>