This paper investigates how and why the appearance of the "immigrant of school age" in Danish basic schooling from 1970-2012 forced and/or inspired Danish teachers to specialize their understanding and professionalize their instruction of this new target group of educational provision and instruction. This period is characterized by a diversification of the population of schoolchildren due to labor immigration, refugee asylums and family reunification in the context of a welfare nation-state facing the forces of globalization (Jønsson & Petersen 2010). Larsen (2010) refers to the act of or desire for professionalization as a matter of "educational optimism" (p. 112, my translation) in the forms of i.e. in-service training. Educational optimism displays a belief that pedagogy and education can make a difference to the life chances of 'ethnic minorities', solve societal 'problems of integration', and as such act on behalf of the imagined collective good (Larsen 2012). This educational optimism is understood in terms of the development of the universal welfare state (Sandin 2012) and its rational engineering of social life (Petersen 1997). Petersen (1997) argues that the government of the collective good in the modern welfare nation-state becomes highly dependent on "the acceptance of expert knowledge as the foundation of a good life" (p. 367, my translation). The paper argues that the act of and desire for professionalization of teachers encountering the immigrant of school age should be understood in terms of the emergent identifications and descriptions of the 'immigrant of school age' as a specific educational (and societal) problem. Edelman (1988) states that problem constructions are historically contingent "constructions of conditions as problems" (p. 13), which work as labels for the perceived threat to the collective good and as signifiers of the appropriate solutions to this threat. The proposition of problem construction to be the inner logic of professionalization of teachers feeds into the analytical framework of the paper, where relations of power/knowledge make up the history of schooling – and in this case the history of professionalization of teachers encountering the 'immigrant of school age'. Hence, the paper aims to write a history of classifications, normalizations, modifications and expertise analyzed through the history of subjects (i.e. foreign-language or bilingual teachers, mother tongue teachers, students, immigrant students, bilingual students, ethnic minority students), practices (i.e. grouping, bussing, exoticizing, integration, Danish language teaching, mother tongue teaching), and discourses/epistemes (i.e. linguistics, anthropology, learning capabilities, culturally deviant behavior, resources, deficiency) (Ball 2013, p. 55). From this analytical perspective, the concepts of profession and professionalization become historically contingent and situated ones to be understood in close relations with the developments of the state (Brante 2005). As such, acts of professionalization are explored as part of the micropolitics of the state, through which professionals (teachers) gain legitimacy in their professional endeavors vis-á-vis the 'immigrant of school age', and at the same time legitimize the micropolitics of the state by means of expert knowledge practices (Ball 2013, p. 74). In other words, practices of in-service training, further education and other forms of knowledge dissemination create a "conceptual infrastructure for professional practice and a set of operationalized discourses" (Ibid, p. 70), which renders state governing possible (Johnson 1995). Decentralized and local experimentation characterizes the educational development of the Danish basic schooling system since the 1970'ties (Hetmar 1991, p. 27). In this developmental process, the professionalization of teachers in regards to the instruction of the 'immigrant of school age' stands out as a highly formative factor in the construction of the 'immigrant of school age' as a specific educational problem. Hence, the paper establishes an archive of documentary material based on the snowball method (Lynggaard 2010), which lets one document lead to the next document, agent or organization until the archive seems saturated. This chain search begins with the professional newsletter, UFE Nyt (newsletter of the organization for teachers of bilingual students, 1977-2006) as it stands out as a key player in the Danish field of educational interventions vis-á-vis the 'immigrant of school age'. The newsletter succeeded to engage teachers, scholars, and representatives of the municipal and ministerial education administrations. I specifically screen the newsletter for editorials, seminar, conference and course announcements, and event reports, which hold evidence to the teachers' aspirations to professionalize their understanding and instruction of the 'immigrant of school age'. Substantial references to other organizations has led me to include the journal, Sprog & Integration (Language & Integration) published by UC2 (Centre for bilingualism and interculturalism). UC2 has been a prominent provider of in-service training and further education of teachers since 1997, which has inspired me to include course descriptions, training manuals and reading lists that are found on the organizations former website by use of the internet library, Wayback Machine (www.wayback.com), or in the private archives of former lecturers. It has also led me to include annual reports of the Royal Danish School of Educational Studies (1970-2000) as it has been a substantial provider of in-service training to Danish teachers. Furthermore, I include the conference programmes of the two annual conferences, Multikulturelle skoler (Multicultural Schools) and Undervisningsministeriets informationsmøde om tosprogede elever (The Ministry of Education's information meeting on bilingual students). Additionally, I include the ministerial newsletter, Det flyvende tæppe (The Flying Carpet) from 1995-2012. The material is indexed and coded (Prior 2003) in three analytical steps. First, I map the institutions of professional training. Secondly, I identify the problem construction of the 'immigrant of school age' and the suggested professional expertise needed to solve the problem. Thirdly, I elaborate a diachronic analysis of the continuities and ruptures in this process of professionalization. The paper expects empirically to identify the subjects, practices and discourses produced in the process of professionalization of teachers encountering the 'immigrant of school age', 1970-2012. Based on this initial coding of the documentary material, the paper aims to establish a historical and analytical dialogue between the identified continuities and ruptures of the professionalization process and the development of the Danish welfare nation-state since 1970. Lastly, the paper will discuss to what extent state governing can be studied through acts of and desires for professionalizing the instruction of the 'immigrant of school age'.