There is growing evidence that the ability to perceive structure is essential for students' mathematical development. Looking at students' structure sense in basic numerical and patterning tasks seems promising for understanding how these tasks set the foundation for the development of later mathematical skills. Previous studies have shown how students use structure sense in enumeration tasks. However, little is known about students' use of structure sense in other early mathematical tasks. The main aim of this study is to investigate the ways in which structure sense is manifested in first-grade students' work across tasks, in quantity comparison and repeating pattern extension tasks. We investigated students' strategies in quantity comparison and pattern extension tasks and how students employ structure sense. We conducted an eye-tracking study with 21 first-grade students, which provided novel insights into commonalities among strategies for these types of tasks. We found that for both tasks, quantity comparison and repeating pattern extension tasks, strategies can be distinguished into those employing structure sense and serial strategies.