Over the past few decades, the debates have shifted from whether to how Computer Science (CS) should be introduced into formal education. Given the diverse ways to introduce CS into formal education, and the struggles many countries have faced, considerably more research is required to provide a framework for effective CS curricular reforms. Effectiveness implies implementing a scalable reform and teacher Professional Development (PD) program that promotes teachers' acceptance of the discipline and sustains changes in their practices to affect student learning and perception. This thesis investigated these prerequisites within a mandatory curricular reform project in the Canton of Vaud in Switzerland. The project introduces CS as a part of Digital Education in the K-12 curriculum through the collaboration between 4 major institutions in a Research Practice Partnership (RPP). The RPP brought together the main reform stakeholders to conceive, pilot and deploy the CS curriculum and teacher PD program to all 93 schools in the region (130'000 students, 9'000 teachers) within a framework that looks to address existing barriers to affecting sustained changes in teachers' practices. In this thesis we focus on the mandatory primary school Digital Education curricular reform where teachers teach all subjects and are generally less interested in teaching CS than specialised teachers. The thesis examines all phases of the reform, from conception to widespread deployment, with inputs from coordinators, trainers, teachers, students and researchers in order to: - Understand how to effectively co-construct a CS PD program with key stakeholders and propose recommendations to improve the outcomes of RPP initiatives. The findings draw from 3 studies where we interviewed project coordinators, trainers, teachers and researchers. - Validate the effectiveness of the proposed curricular reform framework and PD program in terms of teacher perception, short-term and sustained adoption. The validation relies on 3 studies following 350 pilot grades 1-4 teachers for four years, of which two after their PD program. Additional studies then investigated (i) the factors that influence teachers' decision to teach a given CS pedagogical activity through adoption modelling, and (ii) solutions to improve teachers' acceptance of CS. - Investigate how the reform contributes to equity in terms of student perception and learning in one study involving 4 data collections with approximately 13'500 grades 3-6 student- and 320 teacher respondents. Two of these data collections evaluated student learning using the competent Computational Thinking (CT) test, a CT-concepts test we designed and validated through 3 main studies with data from 2'700 grade 3-6 students. - Validate the effectiveness of our adapted cascade deployment model to spread the PD program to all teachers in the region in our final study. The validation concerns the first of three deployment phases and involves 14 teacher-trainers, 700 grades 1-4 teachers and a comparison with the pilot program's outcomes. To conclude, this thesis contributes to validating longitudinally, at a large scale, and through multiple studies, a framework for the sustainable and scalable implementation of CS curricular reforms and their PD program. This framework provides insight which are useful for all stakeholders involved in CS curricular reforms, and will hopefully increase the likelihood of their reforms succeeding.