The realization of curriculum renewals' key ideas in teachers' practices has a reputation for being problematic (Cuban, 1992; Doyle & Ponder, 1997; Coburn, 2003; Fullan, 2007; Otero & Meltzer, 2016). The term slippage is used in connection to implementation (Westbroek, Janssen & Doyle, 2017), although this process is also called, with more empathy for teachers, adaptation (Westbroek, Janssen & Doyle, 2017), enactment (Coburn, 2003) or transformation (Ogborn, 2002).

        A common way to investigate this problem is to examine, for a given project or reform, how closely the curricula enacted by teachers following the renewal activities correspond to the enactments the developers had in mind. Our study focuses on teachers' enacted curricula and investigates to what extent these reflect key ideas from renewals in several decades; we call these ideas curriculum intentions. It also explores what factors may have facilitated these intentions to be expressed in today's enacted curricula. This perspective is inspired by evolution theory, which made us look at curriculum intentions as memes, a cultural equivalent of genes (Dawkins, 2016), expressed in written and enacted curricula over decades. This way of looking at developments is also inspired by approaches like Fullan’s Interactive factors affecting implementation (Fullan, 1989, p.87) or a practicality ethic (Doyle and Ponder, 1973).

        Our case is upper secondary physics education in the Netherlands since 1970, which has been influenced by science curriculum projects in other countries, like PSSC (Physical Science Study Committee, 1960), Harvard Project Physics (The Project Physics Course, 1970), Nuffield Physics (Nuffield Advanced Science: Physics, 1986), and Physik im Kontext (Duit & Mikelskis-Seifert, 2010).

        The twofold research question is: To what extent do enacted curricula in upper general secondary physics education in the Netherlands reflect the intentions of written curricula initiated since the 1970s and which actors and factors influence the expression of the intentions in the enacted curricula? Paraphrased: what key ideas have travelled to today's teachers' practices, and how did they travel? This question reflects the aim of this study: provide those involved in the development and implementation of large-scale renewals with insights that help organize the renewal so that their intentions become reflected in enacted curricula.

        The choice of key ideas started as a hypothesis of what would be representative of renewal intentions, which was checked in publications by six renewals since 1970 and in a meeting of leading developers from those renewals: innovations and formal reforms that concerned the entire upper secondary physics curriculum. This led us to focus on: using contexts, widening the scope of science education in terms of curriculum emphases (Roberts, 1988; Van Driel et al., 2008), coordination with other STEM subjects, advancing concept development, and advancing skills development. We then interviewed 13 current teachers about their enacted curriculum and examined to what extent their intentions reflected those of the renewals. We find that most renewal intentions have taken root in the enacted curricula of most interviewed teachers, prominently advancing concept development and skills development, but also the curriculum emphasis knowledge development in science, and using contexts. Coordinating with other STEM subjects has not been successful.

        To find how these intentions have traveled, we asked the participating teachers what has influenced the way they teach. We also interviewed contemporaries of the renewals about processes and interventions that have supported the propagation of ideas. As a travel route for intentions, teacher education, together with values and beliefs that stem from teachers' own school period, appears very influential for some interviewees. Also, professional development facilities and inspiring colleagues play significant roles. Not surprisingly, we found a strong role of the high-stake national exam system.

The study consists of three sub-studies, the first two on what ideas have traveled, the third on how they have traveled: 1. identifying key ideas in 50 years of renewals 2. identifying key ideas in today’s teachers’ classroom practices 3. identifying the traces during the decades that explain the expression of renewal ideas in the realized curriculum. For the first sub-study, six renewals since 1970 were selected: innovation projects and formal reforms that concerned the entire upper secondary physics curriculum. A hypothesized set of key ideas, addressed in our study as curriculum intentions, were checked in publications by the renewals. A list of quotations from these sources referring to the curriculum intentions was then discussed and adjusted by project leaders and chair persons of the various renewals in a witness conference. The conference report was used to validate the choice of curriculum intentions. For the second sub-study, 13 teachers were interviewed in 2017 and 2018: with and without experience in other roles in upper secondary physics education than a teacher role, e.g. textbook author, from various age groups and with various years of experience. During interviews, the teacher's main activities during a typical lesson and the motives underpinning those activities were mapped. The teachers' responses were coded in ATLAS.ti with descriptions of the curriculum intentions as codes; open coding allowed new intentions to emerge. As a secondary source, an evaluation in 2017 of the most recent curriculum reforms for biology, chemistry, and physics was used, to which ninety physics teachers had contributed (Ottevanger et al., 2018). For the third sub-study, the same 13 teachers were asked to explain the biographical or professional background of their actions. Responses were categorised in elements inspired by the concept of teacher agency (Priestley et al., 2013): life history, professional history, values, beliefs, and structural and material incentives and constraints. Within the incentives and constraints, the resilient system of high-stake national exams and syllabi was distinguished from more responsive elements like school exams, projects, or professional development. As a secondary source, the curriculum evaluation from 2017 was used (Ottevanger et al., 2018). Also, 20 interviews with developers, teacher educators and researchers active from 1980 till today, and documents from those years were analysed, using part of the same categories, but to a large extent other possible how-categories were reconstructed in a grounded way, by clustering observations and advices.

As for the question what has travelled: advancing concept development and widening the scope of curriculum emphases have taken root in the practices of most interviewed teachers, according to their accounts. Most of them use realistic contexts to motivate students, some to support concept development. Advancing skills development is mentioned frequently, but time spent to teach these skills is limited by lack of time. STEM-coordination is mostly limited to research skills. Deviating from renewals' intentions several teachers express a curriculum intention that we call Exercising definitions and procedures, connected to training for exams. As for how ideas have travelled, all interviewed teachers refer to the national syllabus and exam system. Most also refer to professional development communities. Many make connections to values about physics education or the role of the teacher, and to beliefs about effective education. Many mention colleagues as sources for those values and beliefs, and personal biographical elements. For some teachers, teacher educators had a strong influence, others deny any influence. Developers and researchers active since 1980 mention respecting teachers' zone of proximal development: proximal to values and beliefs, but also to the structural and material constraints. Many argue for ambitious curriculum intentions, even if not realisable in the short run, guiding piecemeal development. Several claim that the introduction of the computer in education has given skills development and understanding of thinking and practices of science and technology a strong boost. The hard way of prescribing through national exams and syllabuses only works for content elements, pedagogical approaches can only be recommended. For curriculum intentions that are not supported by that hard way to be expressed in teachers' practices, professional development offers important opportunities, as do safe classroom experiences for teachers, and clarity about strategic key ideas for teachers and their educators.

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