The benefit the outdoor environment has for young children's development is widely documented. However, there is less literature outlining practitioners' experiences of assessing learning in the outdoors and factors which impact the level and quality of assessments undertaken. This study, based on a pragmatic mixed methods approach, undertaken in 9 early years' settings in North Wales, reports the findings of 37 practitioners. The research suggests that assessing children in the outdoors is not used to its potential. Factors impeding the use of the outdoor classroom include: lack of appropriate resources; level of staff expertise; child-staff ratio; adverse weather; and changes to curriculum policy which place emphasis on the formal assessment of children. There appears to be assumptions about learners most likely to benefit from outdoor learning and assessment: boys; children in socio-economically deprived areas; and children with additional learning needs. The paper highlights the need for broader training opportunities for practitioners on planning for learning and assessment in the outdoors that go beyond a single course focus. With creative planning, there is no reason why summative assessments of all areas of learning within the early years' curriculum cannot be done as effectively outdoors as they may be being done indoors.