In this study we have investigated the relation between grade 9 students’ responses to a simple linear equation and a visually similar but proportionally-based linear expression task. Analyses, based on data from the results of a test of 359 Swedish year Swedish students from six diverse schools, drew on written responses to the two tasks. Students giving algebra-based solutions to the linear equation are not only more likely to complete the proportional task but also offer better solutions than students giving arithmetic-based solutions. The results highlight the need for curricula, textbooks and teachers to revisit the place of algebraic equation-solving, whilst also encouraging students to verify their solutions.