Table 1 Framework of the key characteristics of PBL. The six characteristics are as proposed by Krajcik & Shin (2014)

1. Driving question

• One of the most commonly recognised characteristics of PBL (Miller & Krajcik, 2019; Condliffe et al., 2017; Mentzer et al., 2017; Hasni et al., 2016; Krajcik & Shin, 2014; Thomas, 2000; Blumenfeld et al., 1991).

• PBL projects are centred around the driving question: it directs the work, provides the context for it, and reminds the students of the purpose of the various activities included in the project unit (Hasni et al., 2016; Krajcik & Shin, 2014; Hmelo-Silver, 2004; Thomas, 2000; Blumenfeld et al., 1991). The driving question creates continuity and cohesion (Mentzer et al., 2017).

• The end product created at the end of the PBL unit will answer the driving question (Blumenfeld et al., 1991).

• The following features characterise a good driving question in STEM PBL (Hasni et al., 2016):

1. The driving question has an authentic link to the real world experienced by the learners and it is interesting to them.

2. The driving question is open-ended and it challenges the learners to carry out intellectually challenging tasks, whilst considering their age and skill set.

3. The driving question creates the need to understand the central scientific concepts related to the studied subject.

2. Learning goals

• PBL should enable students to learn new topics and skills central to the curriculum (Bell, 2010; Tal et al., 2006; Thomas, 2000). As such, PBL should be the primary instructional method in a course, rather than a separate section of it (Condliffe et al., 2017; Parker et al., 2013). For example, Thomas (2000) states that PBL projects should always teach students new skills and content that are central to the curriculum, and as such projects that are used to enrich the curriculum or revise are not PBL. However, Tamim & Grant (2013) contest this strict view and suggest viewing PBL more broadly, as a continuum.

• PBL tends to consume more time than traditional teacher-centred approaches and as such, it is vital for teachers to feel as though they are able to reach the statutory learning outcomes through it (Krajcik & Shin, 2014).

• To allow the students to gain a deeper understanding of the topic, ask questions and collaborate, the PBL unit should last for longer than one lesson (Krajcik & Shin, 2014; Stearns et al., 2012; Thomas, 2000; Blumenfeld et al., 1991). Whilst a consensus around the idea that PBL should extend over a significant time period seems to exist, it is yet to be specified how long exactly the inquiry should be to qualify as PBL (Condliffe et al., 2017). Chen & Yang (2019) suggest that using PBL for at least two hours per week leads to significantly better academic achievement in students compared to using PBL for less than two hours per week.

3. Scientific practices

• In STEM PBL, students should actively use scientific methods in order to solve and study the driving question (Krajcik & Shin, 2014; Tal et al., 2006; Thomas, 2000; Blumenfeld et al., 1991).

• The PBL unit should allow students to plan and carry out their own research (Mentzer et al., 2017). When developing research questions and methods, students will gain experience in using scientific practices, develop their cognitive skills and build their understanding of the topic (Novak & Krajcik, 2020; Krajcik & Shin, 2014; Thomas, 2000; Blumenfeld et al., 1991).

• Whilst a teacher may choose the driving question, students need to be given the possibility to study their own questions within the scope of the driving question (Krajcik, 2015), as presenting questions is an integral part of scientific research (Chin & Osborne, 2008).

• The scientific practices identified from inquiry-based learning research can be used to describe these practices as found in PBL. Students engage in the following scientific practices within a research project (Pedaste et al., 2015):

1. Orientation into the topic: at the end, students have a problem that they need to solve.

2. Conceptualisation:

a. Presenting research questions

b. Presenting hypotheses

3. Investigation:

a. Exploration (if there is only a research question but no hypothesis)

b. Experimentation (if there is a hypothesis)

c. Data interpretation.

4. Conclusions: students draw them based on the collected data.

5. Discussion:

a. Communicating the results

b. Reflection

4. Collaboration

• During PBL, students carry out research in collaboration with each other (Krajcik & Shin, 2014; Tal et al., 2006).

• Ideally, PBL includes collaboration with experts, companies or parents (Krajcik, 2015; Tal et al., 2006).

• Collaboration is motivating for students (Malone & Lepper, 1987), and it models a scientist’s way of working and allows students to develop their communication skills (Bestelmeyer et al., 2015), and to practice dividing responsibilities and roles (Blumenfeld et al., 1991).

• However, collaboration should be seen as a means to reach the primary goals of PBL; practising science, understanding central concepts, and learning how scientific knowledge is created and used (Hasni et al., 2016).

5. Using technological tools

• Science education should model the importance of computer aided technology in modern scientific research (Edelson, 2001).

• Technology can support student learning through, for example, increased interest, modelling concepts, and strategic support (Tal et al., 2006; Blumenfeld et al., 1991), and it allows the learners to preserve and present knowledge more widely (Edelson, 2001). Learning technologies constitute an important scaffold to students to manage the project activities (Krajcik & Shin, 2014).

• Technology can also support teachers: it can be used to give instructions and support the projects (Blumenfeld et al., 1991).

• Technology can be used to create the artefacts (Tal et al., 2006).

• However, similarly to collaboration, using technology in the PBL unit should in most cases be seen more as a tool rather than the primary goal (Hasni et al., 2016). Whilst technology is useful in PBL and using information technologies appears to improve students’ academic achievement in PBL, it does not necessarily need to be the focal point (Chen & Yang, 2019).

6. Creating an artefact

• In PBL, the learning process is centred around producing an artefact or an end product that answers the driving question (Krajcik & Shin, 2014; Tal et al., 2006; Blumenfeld et al., 1991).

• Artefacts have been proposed to be what differentiates PBL from problem-based and inquiry-based learning (Hasni et al., 2016; Sahin, 2013).

• Artefacts present the students’ cognitive work and their level of understanding (Novak & Krajcik, 2020; Blumenfeld et al., 1991). They are concrete, for example, games, posters, models, plays, websites or drawings (Krajcik & Shin, 2014; Blumenfeld et al., 1991).

• The artefact should (Krajcik & Shin, 2014):

1. Answer the driving question.

2. Reveal the students’ level of understanding.

3. Support students to gain an understanding about the topic when they are creating the artefact.

• The PBL unit could lead to multiple artefacts, but they should culminate into one artefact that answers the driving question (Blumenfeld et al., 1991).

• Creating artefacts is beneficial for learning: students can be expected to learn more effectively when they create external representations of their conceptions (Krajcik & Shin, 2014). Deploying physical objects in the learning process also expands the limitations set by working memory (National Academy of Engineering and National Research Council, 2014). Creating artefacts forces the students to rebuild their understanding constantly (Krajcik & Shin, 2014).

• Ideally, the artefacts should be made public and presented to an audience (Condliffe et al., 2017).

• However, within science education there is a need to conceptualise artefacts better; articles tend to not specify why certain artefacts are specific to PBL, and the artefacts rarely serve a real purpose, which disregards the overarching goal of striving towards authenticity in PBL (Hasni et al., 2016). PBL artefacts should be meaningful (Novak & Krajcik, 2020).