The article reports on outcomes from a study that aims to investigate the role of affordances, level-up and feedback in the web environment Expression Machine in developing the algebra structure sense of tertiary education students. Algebraic substitution is the main procedure involved in the way the software works. Its design and testing methodology are based on the Human - Computer Interaction aspect of Activity Theory. From this approach, the study redefines the notion of algebra structure sense formulated in previous works. Results from the experimental sessions show that some features of the environment favor the development of sutudents structure sense, specifically when they deal with substitution and factorization tasks. At the same time, it was possible to identify aspects to be improved, for instance, adding categories of tasks with increasing structural complexity and less visually salient, which may require a greater cognitive demand from students.