###### Abstract  
The increasing dissemination of virtual reality learning environments (VRLE) compels the elucidation of how these didactic tools can improve their effectiveness at the formative level. The motivation generated in students by a VRLE is revealed as a key factor in achieving meaningful learning, but such a motivation by itself alone does not guarantee the long-term retention of knowledge. To identify the necessary characteristics of a VRLE to achieve an appropriate level of meaningful learning, this paper compares a set of VRLEs created in previous years with a group of recently developed VRLEs, after being used by engineering students. A description of the design process of the both VRLEs groups is included in this paper. Most significantly, analysis of the response of a total of 103 students in a specific survey reveals how a step-by-step protocol system helped improve students' knowledge and retention after one year of using a VRLE. Thus, this study not only demonstrates the importance of using modern development engines when creating or updating a VRLE to achieve student motivation, but also justifies in many cases the use of a step-by-step protocol as a method to improve the long-term retention of knowledge. virtual laboratory; virtual reality learning environment; meaningful learning; design; materials science and engineering. Vol. 100, 2019, 9, 20  
VRLEs: (i) solve the shortcomings linked to overcrowded practical classes; (ii) provide a means to complement student learning experience, given the limited materials testing machine handling time per student in a traditional classroom or laboratory; (iii) offer high-quality visualizations which are not readily feasible in the traditional classroom; (iv) allow instructors to develop ad hoc didactic applications in the virtual environment for reinforcing acquired knowledge; (v) increase students' engagement and motivation in almost any field of study by bringing them closer to a friendly and familiar environment; (vi) improve the quality of education in varied disciplines; (vii) help reduce the cost associated with modern laboratory classes; and (viii) decrease the potential risk of physical harm of students during the handling of real materials testing machines. Furthermore, a better teaching-learning process has been recognized in several research studies [20; 21; 22], leading to better understanding and higher motivation, among other benefits. Despite these advantages, the use of VRLEs in MSE also presents some potential risks, for instance: (i) the user usually feels safe, without realizing the dangers of handling certain types of real machinery [23]; (ii) the student often shows a lack of seriousness, responsibility and care when conducting an experiment in the VRLE [23], which means that the training effectiveness can be reduced; and (iii) the relation between the design of the VRLE and various pedagogical aspects (motivation, ease of use, educational usefulness) may vary over time, forcing the teacher or trainer to keep the software up to date [1; 24]. It is particularly worth noting that the design of a VRLE plays a key role in the development of the teaching-learning process [11; 24; 25]. In fact, according to previous findings, \"a direct relationship exists between the virtual tool design and the motivation generated in the user to keep on using it\" [11].