Sport Education (Siedentop, 1994) was built on the aspiration to provide to students a more meaningful curriculum alternative to the "decontextualized", "one-size-fits-all", "physical-education-as-sports-techniques" approach, which is traditionally present in the practice of many physical education teachers (Kirk, 2013). The large-scale implementation of Sport Education in the national curriculum programs of Australia and New Zealand in the early 1990s brought about renewed teacher enthusiasm that the model could deliver on many of the fundamental educational goals of physical education (Wallhead and O'Sullivan, 2005). The teachers highlighted the high enthusiasm generated by the affiliation and competition features of the model and the possibilities made available for pupils' high engagement in the activities through extensive participation in appropriately modified game practice (Alexander et al., 1993). Despite this enthusiasm, teachers were also skeptical of the effective development of skills and game-play as an outcome of Sport Education, for the model 'relinquishes' to students much of the responsibility for the delivery of the tactical and motor-skills content in the form of peer-teaching activities (Alexander and Luckman, 2001).
Two decades elapsed since the first trials of Sport Education as a curriculum approach and a fully-fledged model is currently gathering wide acceptance from teachers and scholars alike in numerous physical education sites around the world (Hastie, 2012). Concurrently, there is a cumulative extensive body of evidence (from over 100 research papers) that Sport Education, when taught well by committed teachers, can indeed cater for the development of literacy (healthy sports culture) and generate high enthusiastic responses (motivation to participate in sport) by students (Hastie et al., 2011). Nonetheless, although sport-based physical education has historically been the dominant form of physical education (Harvey and Jarret, 2014), evidence of the impact of Sport Education in students' competency in playing games is still "burgeoning and developing" (Hastie et al., 2011, p. 129), as this topic has received less interest of the researchers (Farias et al., 2016).
In Sport Education, consistent with an understanding of sport competency as the intelligent coupling of technical and tactical skills during game-play, "the primary focus is on developing game sense" (Siedentop et al., 2011, p. 26). In agreement, the existing research has measured the program's impact on competency development largely by quantifying pre- to post-test improvements in students' ability to make appropriate decisions during game-play (i.e., decision-making; Hastie et al., 2009). Competency has also been assessed as students' ability to execute motor skills according with the circumstances of the game situations (i.e., skill-execution; Farias et al., 2015) and overall game performance indexes (i.e., ratio appropriate/effective over inappropriate/ineffective game-play; Mesquita et al., 2012). Due to Sport Education's utter concern in promoting high rates of game-play participation, the research has also measured students' game involvement (i.e., volume of play: appropriate/efficient plus inappropriate/inefficient game-play; see Hastie et al., 2009).
Most of the research on Sport Education focused on competency and participation found significant increases altogether in several components of students' game performance (e.g., Araujo et al., 2016) and game involvement (e.g., Wallhead et al., 2013). However, despite these highly positive results, there are two fundamental reasons as why the potential of Sport Education to be used as a prolonged curricular proposal in physical education classes is not yet unequivocally established (Farias et al., 2016). First, though to a lesser extent, a few studies have also found a lack of student improvements in game-play components such as overall game performance (e.g., Mahedero et al., 2015), skill-execution (e.g., Mesquita et al., 2012), or game involvement (e.g., Pritchard et al., 2014). Second, there is evidence from recent large-scale empirical research that students' participation in yearlong programs of Sport Education can have a positive impact in areas such as students' future intentions to participate in extra-curricular physical activity (Wallhead et al., 2013) or in the reshaping of unbalanced power relations towards more equitable learning environments (Farias et al., 2017a). Surprisingly, not a single study has, to date, objectively assessed students' development of game performance and involvement beyond "student experience of a single season of the curriculum" (Wallhead and O'Sullivan, 2005, p. 204). Moreover, the absence of study designs exploring the long-term evolution of competency during students' participation in consecutive seasons of sport (Hastie et al., 2011) is yet to validate the conceptual cornerstone of game-based pedagogies. Namely, the potential for transfer of performance across games within a same category (Mitchell et al., 2013).
Therefore, in line with the reasoning presented so far, the purpose of this study was to examine students' development of game performance and game involvement during participation in three consecutive seasons of invasion games.
Participants and setting
Setting: The setting of this study was a middle school located in a northern county of a southern European country, which included classes from the fifth to the ninth grades. This was an average-sized school with around 750 students enrolled in compulsory physical education lessons. The students were required to complete a three-terms (October to June) program which included weekly participation in one 45-mins session and one 90-mins session. Most students in this school came from working class families from low to middle income households, about a fifth of the cohort benefited of free school meals, and the representation of ethnic-minority students within the school was approximately 12%.
Selection of the participant students: The class that participated in this study was composed of 26 students of the seventh grade (10 girls and 16 boys, average age 12.3 [+ or -] 1.3). In agreement to the procedures followed in other research (MacPhail et al., 2008), 10 participant players were selected for Game Performance tracking across the school year through a nominal group technique. Figure 1 illustrates the procedural steps taken in the selection of the 10 players whose Game Performance was examined. The key selection criterion was that the 10-players' cohort played against each other in all initial and ending lessons of each season (10 players: Team 'A' and Team 'B', three boys and two girls per team).
Teacher: The teacher in this study was a member of the research team who had been a former physical education teacher in the school where this research was conducted. He was deemed a physical education specialist (12 years of experience) by the teaching community and he had previous experience implementing both Sport Education and game-centered approaches (e.g., Tactical Games model).
Permission to conduct the study was obtained from the host University's Ethical Committee Review Board. For gathering consent for data collection, the first author participated in formal meetings with the school's principal and members of the physical education department, the participants' legal guardians, and the participant students. The researcher explained to all stakeholders in a detailed and truthful manner the goals of the research project, the nature, focus, and duration of data collection and means of dissemination of the research findings. Both the legal guardians and the students selected for the study were formally addressed in a classroom context and informed of the nature of the project, the pedagogical and research procedures, the main goals and features of Sport Education, and the responsibilities inherent to role-playing. All of those involved in the project signed informed consent forms.
The seasons, learning content, and instructional processes: All members of the research team were experts in Sport Education and other instructional models (e.g., the Tactical Games Model), and had an extensive record of prior investigation of the model and experience in teaching physical education both at a school and higher education levels. In agreement, the decisions related to the content addressed in the teaching units, means of content development, type of roles and levels of responsibility assigned to students, nature of the instruction employed by the teacher, and strategies used to mediate peer-teaching activities, were collectively taken as a team and continually reflected upon and adjusted. Moreover, based on the daily examination of the videotape images of all the lessons, there was kept a daily record in the format of a field diary that recorded in a systematic and chronological manner all the procedures mentioned above. Table 1 provides details on the content addressed in the seasons, while the following sections inform about the instructional processes employed.
The sport education seasons: As required by the school's physical education curriculum for the seventh grade, the teaching units included three consecutive sport-based units. In this case, the units were taught within a Sport Education framework and consisted of basketball (20 lessons of 45-mins), team handball (16 lessons of 45mins), and football (18 lessons of 45-mins).
In the first lesson of the first Sport Education season (basketball), as a method of team selection suggested by Siedentop (1994), six student-coaches (three boys and three girls) were voted to constitute a selection committee which worked with the teacher to allocate all students to six heterogeneous, but balanced teams (Teams 'A' to 'F'). The teams contained similar number of boys and girls and of...