Historical reasoning helps students understand the dynamics between different time periods. A group of teachers, teacher trainers and researchers collaborate on developing a toolkit that helps teachers to focus on developing historical reasoning of their students, starting out from a CHAT perspective. During the school year 2016-2017, 11 teachers of students aged 9-12 took part in a research project to design history education. They were supported in this effort by teacher trainers and researchers who visited them in their classrooms regularly and discussed their teaching during meetings. The whole research group was aimed at improving a toolkit for historical reasoning so that other teachers can use this as well. Important subjects in the meetings were the use of exploratory talk in students’ historical research, connecting the past, present and future, and the use of ‘big ideas’ (like power, communication and inventions). Video observations of lessons, interviews with children and portfolios of both teachers and teacher trainers provided insight of both the development of historical reasoning of children, as well as the capacities of teachers to design lessons. From the preliminary results, we can see that teachers find it interesting to search for historical questions into different topics, together with children. At the same time, teachers feel it is challenging to engage in conversations that result in the historical reasoning of students. They needed support in asking the right types of questions and guiding conversations in such a way that historical reasoning is evoked in children.