This chapter suggests the use of formative assessment in inquiry lessons as a helpful source of positive personal capacity beliefs for both teachers and students. The challenge most commonly experienced when first using inquiry learning methods is that pupils and even teachers become uncertain of their abilities to use inquiry and ‘give-up’ on it. With the use of formative assessment combined with conscious efforts to increase self-efficacy among students, teachers can help provide students with the confidence and motivation to engage in inquiry methods. Such student engagement can in-turn affirm teachers’ inquiry teaching efforts and raise the likelihood that they will continue to improve them. We see inquiry methods as the motor for changing teacher practice and formative assessment methods combined with capacity beliefs as the fuel that keeps the motor running. The central position of the chapter is how suitable assessment methods for inquiry based science education can enhance teachers’ capacity beliefs about their ability to use these methods in their teaching.