Statistical association between two variables is one of the fundamental statistical ideas in school curricula. Reasoning about statistical association has been deemed one of the most important cognitive activities that humans perform. Students are typically introduced to statistical association through the study of the line of best fit because it is a natural extension of their study of linear equations in mathematics. This is predominantly true for students in the United States; for example the authors of the Common Core State Standards for Mathematics (CCSSM) ask that students in eighth grade learn about linear equations, linear functions, and the line of best fit. A learning trajectory for linear regression study begins with students finding and studying an informal line of best fit, which refers to the idea that students are fitting a line, by eye, to data displayed in a scatterplot, without making calculations or using technology to place the line. In this article, the author presents how students can explore six tasks to develop criteria for finding an informal line of best fit.