Inquiry-based learning (IBL) has been considered an essential component of science education for several years (e.g., Abrams et al., 2008). A considerable number of studies has shown that IBL positively influences students’ attitudes towards science as well as their learning of science (e.g., Blanchard et al., 2010; Furtak et al., 2012). The skills addressed by IBL meet the requirements stated in science standards and curricula (e.g., NGSS Lead States, 2013) and foster the acquirement of scientific literacy (Roberts & Bybee, 2014). Depending on learning objectives, degree of openness, and instructional support, IBL can be implemented in a variety of forms (e.g., Abrams et al., 2008; Blanchard et al., 2010). Open inquiry settings (OIS) that give students the opportunity to pursue their own questions and design and conduct investigations in a self-determined (but scaffolded) manner seem to be particularly motivating (Jiang & McComas, 2015). Beyond that, OIS do not only foster students’ ability to apply science concepts and methods independently, but also address their diversity by allowing for individual learning paths (e.g., Abels, 2014). However, many science teachers are sceptical about the implementation of OIS, fearing that conceptual learning will be neglected (e.g., Hofer et al., 2018).

In the field of science education, conceptual learning is traditionally determined by assessing which and how many concepts students have acquired during a certain period of time or by a certain point in time, how elaborated these concepts are, and how they are related to each other (Amin et al., 2014). This perspective on conceptual learning is what Scott et al. (2007) call acquisition metaphor. According to this, conceptual learning is a process of acquiring and accumulating “basic units of knowledge [concepts] that can be accumulated, gradually refined, and combined to form ever richer cognitive structures” (Scott et al., 2007, p. 5).
In OIS, however, science concepts are not presented in an isolated way, detached from the context, but are developed by the students as part of the inquiry process. Learning in OIS is therefore rather a process of developing participation in the practices of a specific community (participation metaphor) than acquiring and accumulating concepts. Consequently, established assessment tools and methods for investigating conceptual learning are only applicable to a limited extent (Cowie, 2012) resulting in challenges concerning educational research.

Data from PISA 2015 indicate that IBL and especially OIS still rarely find their way into European science classrooms. Beyond that, there seems to be a negative correlation between the frequency of implementing rather open instructional approaches, such as OIS, and students’ level of scientific literacy (e.g., Forbes et al., 2020). To put it in a nutshell: The more often students learn in OIS, the lower their scientific literacy. These results, however, are based on students’ self-reports and do not consider any further information concerning the implementation of OIS. Other studies investigating students’ outcomes in IBL (see e.g., meta-studies by Furtak et al., 2012; Lazonder & Harmsen, 2016) do either focus on procedural and epistemic skills or are limited to IBL with lower degrees of openness. Yet, there seems to be only little empirical evidence about students’ conceptual learning in open inquiry settings.

Hence, this study aims at identifying empirical studies on OIS in science education and synthesising what science education research actually knows about students’ conceptual learning in OIS. In so doing, the following research question is to be answered:
What are the findings on conceptual learning of primary and secondary science students in OIS that have been obtained from empirical studies so far?

To answer the research question, we conducted a systematic literature review according to the procedure suggested by Fink (2019). For this purpose, we started with a keyword-based search on ERIC database and Web of Science (WoS), as these two databases represent a full indexing system focused on education (ERIC) and the most “recognized”, high-ranking papers (WoS). To determine the keywords, we derived central terms from relevant literature, searched literature databases for synonymous terms, and discussed the list of keywords with experts in the field. Finally, the keywords were organised in three components: (1) conceptual learning, (2) IBL / OIS and (3) science education. For example, we entered the following input for the component conceptual learning into ERIC database using Boolean logic: (concept* OR content* OR subject*) AND (learn* OR develop* OR understand* OR construct* OR build*). The keyword-based search (for titles and abstracts) resulted in a number of N = 596 records. To be considered in the further review process, papers were required to meet the following eligibility criteria (Rethlefsen et al., 2021): • Level of science education: primary or secondary school • Publication date: since 2003 (last 20 years) • Publication language: English • Publication type: only peer reviewed original research papers • Accessibility: online accessible By applying these criteria as filters to the databases, the number of records was limited to N = 163. To prove the content-related eligibility, the remained records were screened by title and abstract in a first step (resulting in N = 30 records) and by full-text read in a second step (resulting in N = 8 records). The finally selected papers were then analysed in terms of study context, design and methodology (descriptive analysis) and study results and findings (qualitative analysis). As we were interested in both the WHAT and the HOW, the qualitative analysis was guided by the following questions: • What do students learn (limited to the conceptual domain)? • Is it possible to identify relationships between students’ conceptual learning and the way of how OIS are implemented in a particular case? • What are the theoretical models and frameworks (regarding conceptual learning and OIS) these studies rely on? The whole review process was documented following the reporting guidelines stated by the PRISMA group (Rethlefsen et al., 2021).

The eight studies included in the full-text analysis were conducted in six countries (three European) and were published between 2011 and 2020. Five of them were quasi-experimental studies (three with control group), two design-based studies and one case study. In the quantitative studies, conceptual learning was considered exclusively from the perspective of acquisition, whereas the qualitative studies also included aspects referring to the participation perspective (Scott et al., 2007). This was also reflected in the data collection methods – pre-post-test questionnaires vs. triangulation of diverse data material. In general, it can be stated that OIS have a high amount of “active learning time” and positively influence students’ conceptual learning. Well-structured and scaffolded OIS were proved to result in significant gains in conceptual knowledge, being even more effective than instructional lectures. However, it was emphasised in all studies that the need for scaffolding in OIS increases with the complexity of both concepts and the learning product (e.g., portfolio, poster) – particularly for students with little prior knowledge. Introducing tiered scaffolds and providing feedback enable students to deal with new concepts and embed them in their existing conceptual knowledge, hence, contribute to increasing and stabilising learning effects. Beyond that, in-depth analyses of qualitative data showed that OIS might allow for individual learning paths whilst still creating a common knowledge base. The results of this review study show that there is still a lack of empirical data on conceptual learning in OIS. The study findings partly agree with the PISA data, but also contradict them in several aspects. Additionally, the complexity of OIS comes with methodological challenges: loss of multilayeredness and multiperspectivity in quantitative studies vs. limited feasibility and comparability in qualitative studies. Thus, to allow profound conclusions about conceptual learning in OIS, more and methodologically diverse studies are required.

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