With a focus on epistemology, this paper discusses what pattern generalisation as an algebraic activity involves. Further, it presents a review of empirical studies where a pattern-based approach is used to teach algebra. This shows that students' problems with establishing algebraic rules from patterns and tables can be explained by: 1) difficulties caused by students' use of invalid methods to identify explicit formulae; 2) difficulties caused by students' tendency to focus on recurrence relations; and 3) institutional constraints. As an alternative to a traditional task on a shape pattern, the paper presents an epistemological model designed to implement the equivalence statement: 1 + 3 + 5 + L + 2n − 1 = n^2 .