Since 1996 the Brazilian Educational System has been establishing a set of national educational policies regarding the proposition, implementation, and assessment of national curriculum standards for the elementary, medium and high schools, known as The National Curriculum Guidelines (NCG). These guidelines take into account all acknowledged subject matters for each grade and level, as well as pedagogical guidelines and assessment considerations. They also establish cross-themes for the teaching and learning process. Focusing on social issues, the cross-themes vary significantly from the different fields of knowledge usually present in the school curriculum. Environment, ethics, cultural plurality, health and sexual education are the elected cross-themes for the elementary school. This study is part of a broad seven-year research (1996-2003), involving a partnership between a public university and an elementary public school from the city of São Carlos/SP/Brazil, aiming to improve the quality of teaching and schooling processes through an in-service teacher education program developed in the workplace. Its research questions were: How do elementary schoolteachers 'translate' the knowledge base for the first four grades of the elementary school - collectively constructed by means of collaborative work involving a university-public school partnership? How does this 'translation' address the knowledge base in the explanation of the curriculum contents having the NCG's cross-themes as its axis? The participants were 23 professionals from the school and 5 researchers from the university. The adopted theoretical orientations were drawn from literature regarding: teachers' professional development processes; teachers' thinking; inquiry and collaboration in teacher education; communities of learning; models of knowledge base for teaching and the pedagogical reasoning process; reflection considered as a conceptual orientation; learning-in-context theory, and organizational learning. Methodologically the research was conducted via teaching and learning experiences, here considered as educative and investigative tools: projects developed collaboratively by schoolteachers and researchers shaping a community of learning. These experiences were diverse and encompassed different aspects of the teacher's work in order to allow the investigation of the teachers' professional development processes, their ways of thinking and constructing their practices, as well provide for the promotion of such processes. The data sources were: participant observation; oral narratives; individual written reports; group written reports, diary entries, teachers' plans, teaching cases, individual and collective interviews; activities developed by the teachers, and students' productions. This communication addresses four of these experiences, having, as their axes, the NCG's cross-themes: environmental issues, cultural plurality, and health and sexual education. The data highlighted the crucial importance of the construction process of pedagogical content knowledge in the professional development of schoolteachers. Three tendencies could be observed. Some of teachers developed all the experiences in an integrated way, contemplating the different subject matters and moving through them during all the experiences. We consider this tendency to closely match the meaning of the NCG cross-themes. Some of the teachers developed the experiences in an additive way, dealing with the cross-themes in each subject matter separately. A third group, composed by only a few teachers, seems not to understand the concept of cross- themes, as well as how they might be developed. These teachers seem to be guided only by activities that would somehow guarantee the students' learning. The teaching and learning processes observed were not linear, continuous, uniform and predictable. Exposition to the analysis of peers, as well as the existence of common themes that directly involved all the schoolteachers, the existence of time for discussion, the creation of a community of learning in the workplace, the creation of space and opportunities destined to put under proof their practices, facing multiple possibilities of failure, can all be considered factors that contributed to the success of this experience, regardless of the difficulties and peculiarities of the teachers´ professional learning processes.