An extensive literature provides evidence that Teacher Self-Efficacy (TSE) is a powerful predictor of student achievement (Armor et al., 1976; Tshannen-Moran et al., 1998 , Hoy & Spero, 2005). The relationship between TSE and student outcomes has been studied for decades. It is now quite well known that TSE is positively associated with teacher behaviour and attitude in the classroom (Bandura, 1997). For example, teachers who strongly belief in their instructional efficacy are more likely to implement innovative strategies for teaching (Guskey, 1988), to devote more time to academic activities, to have high expectation for student learning or to persist with student who encounter difficulties (Gibson & Dembo, 1984; Bandura, 1997).

                If most studies confirm the positive effect of TSE on student achievement, surprisingly no clear consensus has been found on the best way to measure this concept.  Indeed, empirical studies often rely on different type of measurements. As an illustration, McGee and Wang (2014) provide a complete listing of self-efficacy measurement instruments. Since the birth of the concept with the RAND study (Armor et al., 1976), they identify thirteen existing different scales in the literature. The growing body of measurement instruments is a very good illustration of the persisting difficulty to conceptualise and measure TSE (Sodak & Podell , 1996  ; Tshannen-Moran et alii, 1998 ; Skaalvik & Skaalvik, 2009).

                This paper aims to clarify the meaning of TSE by reviewing the literature of the concept and comparing different scales commonly used in the literature in order to understand its underlying constructs.  To do so, we decide to focus our attention on three main TSE measurement instruments.

                The first one is the Teacher Efficacy Scale (TES) developed by Gibson and Dembo (1984). Although, initially based on the theoretical framework of Rotter's Locus of Control (Soodak & Podell, 1996; McGee & Wang, 2014; Hoy & Spero, 2005), Gibson and Dembo interpret the two factors of their scale with Bandura's self-efficacy theory (Gibson & Dembo , 1984). These two theoretical foundation (Rotter's and Bandura's) that have guided the construction of this scale tends to create much confusions about the nature of its underlying constructs (Guskey & Passaro, 1994). The second scale that we choose to analyse is the Teacher Sense of Efficacy Scale (TSES) of Tshannen-Moran and Woolfolk Hoy (2001). This scale is aligned with Bandura's idea that Teacher Self-Efficacy is a multi-faceted construct that should be specific to tasks of teaching (Bandura, 1997). Indeed, according to Bandura's theory, Teacher Self-Efficacy is not necessary uniform across the many different types of tasks that characterised teachers work life (Bandura, 1997; Hoy & Spero, 2005; Tshannen-Moran & Woolfolk Hoy, 2001). Therefore, the TSES is link with three different teaching domains: instructional strategies, classroom management and student engagement. This scale is often considered to present the most unify and stable factor structure (Hoy & Spero, 2005; McGlee & Wang, 2014). Finally, because teacher self-efficacy could also be specific to subject matter (Bandura 1997 ; McGee & Wang 2014), the third scale that we will discuss in this article is an adaptation of Self-Efficacy for Teaching Mathematics Instrument (SETMI) created by McGee and Wang (2014). Since mathematics content is country specific, we have adapted this scale to the French-speaking Belgian mathematic curricula in order to match the context of our investigation sample.

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