The nature of scientific knowledge or nature of science (NOS) represents some interdisciplinary contents of the science curricula about what science is and how science works as a way of knowing and explaining the natural world, which has been elaborated from interdisciplinary perspectives (history, philosophy and sociology of science and technology, and others). The central issue of NOS is knowledge construction and validation, which includes the epistemological principles underlying scientific explanations and the institutional and societal issues involving the relationships and interactions within the community of scientists (internal sociology), the mutual influence between society and the techno-scientific system (the external sociology of science), and the general interactions of science, technology, and society (STS), where education, communication, innovation, scientific policies, socio-scientific issues, etc., emerge. Altogether, these aspects make up NOS (Lederman, 2008; Vesterinen, Manassero-Mas, & Vázquez-Alonso, 2014).

Understanding NOS is a key component of the scientific literacy for all and a perennial goal of science education (Hodson, 2009; Millar, 2006), whose pursuit has developed innovative science curricula to teach NOS contents in many countries (McComas & Olson, 1998; NRC, 1996). The Next Generation Science Standards (NGSS, 2013) recently provided a reinforced, simplified, and renewed curricular vision of NOS by grouping NOS contents into scientific practices and transversal contents. However, some theoretical controversies about NOS conceptualization and the most appropriate NOS issues for curricula still add some complexity (Erduran & Dagher, 2014). Beyond controversies, NOS is widely acknowledged as a meta-cognitive, multifaceted, and dynamic realm with affective components and values related to science practice. Thus, teaching NOS represents a hard innovative challenge due to its meta-knowledge status (i.e., scientific knowledge is tentative) and complex philosophical (coordination of evidence and explanation) and sociological (scientists scrutinize findings) grounds (Adúriz-Bravo, 2014; Matthews, 2012).

The Spanish secondary science curriculum specifies some NOS contents and attainment goals through a block on scientific research, common for all science subjects. However, the overall contents, textbooks, and teaching practices are quite traditional and neglect the teaching of explicit NOS contents in Spanish science education and pre-service teacher education. The innovative challenge for Spanish science education is twofold, teaching NOS issues to all students and educating teachers on NOS. Thus, this study aims to train pre-service Spanish teachers to improve their NOS conceptions and their professional development and to motivate them to teach NOS within the classroom, through an experience with innovative NOS contents about scientific investigations (Manassero-Mas, Bennàssar & Vázquez-Alonso, 2018).

Teachers and Teaching the Nature of science

Innovations usually generate some teachers’ resistance to change, which poses a general educational challenge. In the case of NOS teaching, the literature adds two additional hindrances: teachers’ uninformed NOS beliefs and lack of teaching resources (Heering & Höttecke, 2014; Donnelly & Argyle, 2011).

For years, research consistently and repeatedly shows that most teachers hold uninformed and poor NOS understanding (Apostolou & Koulaidis, 2010; Bennàssar, Vázquez, Manassero & García-Carmona, 2010; Celik & Bayrakçeken, 2006; Ma, 2009), which is the greatest obstacle to teaching NOS (Irez, 2006; Lederman, 2008; Vázquez & Manassero, 2012). The NOS profile of Spanish secondary science teachers leads to an unsatisfactory competence to teach NOS. Further, the differences between Spanish novices and experienced teachers are non-significant, which means that teaching practice is ineffective for improving teachers’ NOS understanding (Vázquez-Alonso, García-Carmona, Manassero-Mas & Bennàssar-Roig, 2013). As it is impossible to teach the contents that teachers do not master, teachers' appropriate understanding of NOS constitutes a necessary condition for quality NOS teaching (Tsai, 2007).

The review of Deng, Chen, Tsai, and Chai (2011) endorses explicit and reflective instruction as the pedagogical conditions for quality and effective NOS teaching, a claim also supported by others (i.e., Lederman, 2008). Explicit teaching refers to the intentional treatment of NOS topics, which involves full educational planning and explicit application in the classroom, and goes beyond indirect instruction (Abd-El-Khalick & Akerson, 2009; Lederman, 2008). Reflection means that learners must perform meta-cognitive and reflective activities about NOS, such as exploration, analysis, discussion, debate, conclusion, argumentation, decision making, etc. (Kucuk, 2008; Deng et al., 2011).

Some NOS teaching resources have currently been developed in different research studies with pre-service teachers. Wong, Hodson, Kwan and Yung (2008) developed real-life context instructional resources in severe acute respiratory syndrome for pre-service teacher education, which explicitly emphasized several aspects of NOS and authentic scientific inquiry (the mutual impact of science and technology, the humanistic character of scientists, and the inseparable links between science and the social environment). Likewise, Adúriz-Bravo and Izquierdo-Aymerich (2009) applied to pre-service science teachers a research-informed instructional resource about the discovery of radium by the Curies. The teachers solved tasks about three NOS ideas (the distinction between discovering and inventing, scientific modeling via abduction, and the hagiographic treatment of Madame Curie) and developed debates about the tasks. The historical scientific controversies have also inspired some educational resources to teach NOS to pre-service teachers. For instance, García-Carmona and Acevedo-Díaz (2017) drew on the Pasteur-Liebig controversy on fermentation to improve teachers’ understanding of scientific theories and scientific interpretations; Aragón, Acevedo-Díaz, and García-Carmona (2019) used the Semmelweis case as a didactical tool to impact teachers’ ideas on scientific observations, inferences, creativity, methodology, hypothesis, theories, communication, policy, and scientists’ personality. Suzuri-Hernandez (2010) elaborated six historical cases, ranging from physics to life sciences, and developed readings and questions to teach the difference between facts and interpretations and controversies among scientists. These and other studies emphasize the effectiveness of the history of science to educate teachers on NOS.

Many studies tested the effectiveness of teaching resources and methodologies to change teachers’ NOS views. Kucuk (2008) trained twelve pre-service elementary teachers through an explicit/reflective STS course, and the teachers improved their NOS understandings, except for the relationship and distinction between theories and laws. Bell, Matkins, and Gansneder (2011) researched the impacts of climate change and global warming across two contexts (standalone vs. situated within instruction) and two instructional strategies (implicit vs. explicit) in 75 pre-service elementary teachers. The teachers under explicit instruction made statistically significant gains in their NOS views regardless of the topic context, and the participants under explicit instruction as a stand-alone topic could appropriately apply their NOS understandings to new situations. Tsai (2006) also found that instruction about conceptual change was more helpful than direct instruction to change teachers’ views about science. Lotter, Singer and Godley (2009) proved the influence of a secondary science methods program in secondary science pre-service teachers’ views and enactment of NOS and inquiry-based instructional practices, through multiple low-stake teaching and reflection experiences (similar to the multiple tasks proposed here). Wan, Wong and Zhan (2013) interviewed twenty-four Chinese science teacher educators about their NOS teaching conceptions, and the educators suggested five key dimensions (value of teaching NOS, NOS content, incorporation of NOS instruction in courses, learning NOS, and the role of the teacher) that provide a useful framework to interpret the practice of teaching NOS. Overall, these studies suggest that the effectiveness of explicit and reflective pedagogy depends somewhat on the specific NOS idea and the teaching context. Finally, Cofré et al. (2019) reviewed the state of the art, concluding that the interventions lasted over one semester for pre-service teachers, that some aspects of NOS (empirical basis, observation and inference, and creativity) are easier to learn than others (tentativeness, theory and law, social and cultural embeddedness, subjective aspects of NOS and “the scientific method”), and that future investigation should focus on the differences between the easy and difficult aspects of NOS and on assessing the effectiveness of different kind of courses.

Rationale

Science teacher education on NOS in Spain is almost inexistent due to the poor definition of NOS contents in science school curricula and the lack of further specific prescriptions on NOS for pre-service teacher education. Hence, this study aims to fill in this gap with the development of an educational experience about scientific investigations, which follows and applies procedures and tools of previous research studies, such as the explicit and reflective framework to improve teachers’ NOS beliefs, dispositions, and pedagogical professional development (Abd-El-Khalick, 2012; Bennàssar et al., 2010; Vázquez-Alonso & Manassero-Mas, 2019; Suzuri-Hernandez, 2010; Vázquez, & Manassero, 2013a).

Two general frameworks of learning and teacher development are also taken into account. On the one hand, the explicit goal of improving teachers’ NOS beliefs considers learning as a conceptual and metacognitive change (Abd-el-Khalick & Akerson, 2009). On the other hand, teacher learning has recently been established through a global model of teacher professional development, which involves a continuous change in learning, planning, and teaching specific topics (NOS) specifically (explicit and reflective) for a specific purpose (science literacy), which, in turn, means enhancing specific students’ NOS understanding at a specific time (Gess-Newsome, 2015; Mesci, 2020). This study joins the "7E learning cycle" structure as a NOS pedagogical model, which deploys the explicit and reflective activities across seven learning milestones: elicit (previous ideas), engage (learners), explore (contents), explain (conclusions), elaborate (results), extend (consequences), and evaluate (Eisenkraft, 2003).

Further, this study aims to research the empirical efficacy of the educational experience to improve teachers' NOS understanding of scientific investigations, as a way towards teacher professional development on NOS. The explicit and reflective framework was developed around some short and specific readings about controversial cases of the history of science that align with previous research (Aragón et al., 2019; García-Carmona & Acevedo-Díaz, 2017; Heering & Höttecke, 2014; Klassen & Froese-Klassen, 2014; Rudge & Howe, 2009). The pre-service teachers’ professional development was expected to expand around the elaboration of the readings, the answers to some questions about scientific investigations, the development of a lesson plan, and the self-reflection about their own thinking (Sprod, 2014). The research questions are: What are prospective secondary science teachers’ prior NOS beliefs about scientific investigations? How do teachers change their prior NOS beliefs as a result of the experience? Is the experience effective to improve teachers’ professional development on NOS?