SellSTEM will train a new generation of early stage researchers (ESR) to bring fresh thinking to the twin issue of low enrolment and gender imbalance in STEM education and careers by addressing deficits in spatial ability among young people across Europe. A key factor of intelligence, spatial ability is strongly related to achievement in and attraction towards STEM learning yet is underdeveloped among many young people in Europe. The large gender gap in spatial ability in favour of males means girls are over-represented in the low spatial ability group and more disadvantaged in STEM learning. ESRs will be trained to collect spatial ability data from children in Europe, measure their relation to academic performance and career choice and analyse interaction by gender, region and socioeconomic status. ESRs will create ways to develop spatial ability among children through online learning, tactile activities, integrated with other subjects and through project-based learning including maker space workshop. ESRs will work with teachers and teacher educators to identify barriers and enablers to developing spatial ability so they can provide sustainable classroom solutions to increase the spatial ability of children beyond existing levels. Education policy and curriculum design will be critiqued against latest research on cognitive development. Improved policies and curricula will be produced along with strategies to change teacher education and teaching practice. Guides for teachers to assessing spatial ability and classroom teaching activities for different age groups will be developed so teachers can assess and promote growth in spatial ability especially among girls. SellSTEM ESRs will produce new knowledge and methods to promote spatial development, increase STEM enrolment and reduce gender imbalance and help to open up an important research topic in Europe. In this way, SellSTEM will and directly support the EU agenda for growth and jobs both now and into the future.