With the introduction of the Swedish national curriculum, Curriculum for the compulsory school, preschool class and school-age educare, (Skolverket, 2017a), Swedish pupils will receive a more scientifically influenced history education in which they learn historical thinking. A requirement for this education is that pupils develop their reasoning abilities in their subjects. This survey takes its point of departure in this changed requirement, specifically in the skill of written reasoning. The article highlights seven planning sessions and one concluding conversation during which two fifth-grade teachers planned their history lessons with a focus on written reasoning. The aim of this work is to contribute to teachers' conceptions of how teaching can be designed to help pupils develop this ability. First, to gain insight into the teachers' conceptions of written historical reasoning, participant observation and a phenomenographic analysis of the data were carried out. The results show that teachers conceive of written reasoning in history as a) understanding the historical content, b) the active use of content concepts, c) shifting between time and room perspectives and d) perceiving text qualities. A thematic analysis was then conducted, and its results showed that teaching, according to the teachers, needs to include the use of study material, be visually supportive, collaborative, reflective and attentive to text structure and language patterns. In summary, the results reveal the complexity of planning history lessons for younger pupils, who should be given the opportunity to develop both historical thinking and the ability to conduct written historical reasoning.