“…The term "group" has been used widely in these studies and referred to different units, including pairs (e.g., Harskamp, et al, 2008), small groups (e.g., Gnesdilow et al, 2013), classes (e.g., Friend, 2006), programs (e.g., Richardson et al, 2003), or even camps (e.g., Hughes, et al, 2013). Methods-wise, some researchers simply compared single-gender and mixed-gender units (e.g., Friend, 2006); and a few others systematically varied the gender composition of student units (e.g., 25%, 50%, 75%... female; Dasgupta et al, 2015). Also, importantly, these studies have measured a wide variety of variables, such as student identity (e.g., Hughes et al, 2013), attitudes (e.g., Watson & Lyons, 2009), competence (e.g., Häussler & Hoffmann, 2002), interest (e.g., Hughes et al, 2013), self-efficacy (e.g., Dasgupta et al, 2016), engagement (e.g., Bennett et al, 2010), career aspiration (e.g., Dasgupta et al, 2016), and achievement (e.g., Baker, 2005).…”