The present study focuses on challenges to the work of teachers as a result of a Swedish educational reform that mandates schools guarantee pupils receive early learning support concerning reading, writing, and number sense. The outcome of reforms is connected to how teachers achieve agency in their work , and we use the ecological model of teacher agency as an overarching theoretical framework and analytical dimension. The study involved interviews with 14 teachers, and the focus was on a) how teachers identify pupils in need of support and how this support is carried out, (b) how teachers would like this identification to be carried out, and how teachers would like to support pupils with weak number sense. Teachers described a 'dilemmatic space' (cf. Fransson and Grannäs 2013), which affects how they achieved agency in developing pupils' number sense. The dilemmatic space described by teachers in this study is framed by necessary priorities pertaining to the cultural, structural, and material conditions of the current situation. According to the study's results, whether teachers should perform the assessment merits discussion. The study concludes there is a risk that conducting assessments and offering support risks cancelling each other out.