This study investigated the role of online applets in early algebra lessons. The effect of two different types of intervention modules on developing students' early algebraic thinking abilities was compared. The first intervention module involved the use of open applets and real-life contexts (open-real). The second intervention module involved the use of closed applets and pure mathematics contexts (closed/pure). "Open" applets are considered to promote more explorative ways of working with mathematical ideas, whereas "closed" applets are considered to guide students' ways of working through more sequential, step-by-step approaches. Real-life contexts present everyday applications of mathematics, where pure mathematics contexts focus on the mathematical concepts and procedures, with no reference to the way they could be associated with real-life situations. Nevertheless, both intervention modules followed an inquiry-based approach. The total number of the participants were 96 young students of Grade 5 with an average age of 10,5 years old. These students were tested through a pre- and a post-test on early algebraic thinking. The test involved three categories of early algebra tasks: generalized arithmetic, functional thinking, and modeling languages. Data from the pre- and post-test comparison showed that students who participated in the "open/real" module had a statistically significant higher improvement in functional thinking compared to students who participated in the "closed/pure" module. There were no statistically significant differences between the improvement of the two groups of students in generalized arithmetic and modeling languages. These findings offer pedagogical implications in respect to the design of early algebra lessons that take advantage of the affordances of available educational technology.