The inclusion of all children in regular classrooms is an important aim in many European countries. For the implementation of inclusion some children rely on support via learning and support assistants. Despite the benefits assistants provide by enhancing student access and progress, assistants' support has also been criticised for contributing to more exclusive than to inclusive processes in class. A necessary precondition for enhancing inclusive processes is the assistants' extension of professional knowledge and competence. This study aims to evaluate the effects of a developed online tool for assistants' professionalisation on the collaboration with teachers and parents. Moreover success factors in assistants' work are identified. The quantitative study sample consisted of 70 assistants, teachers and parents. Focus group interviews with nine assistants and teachers were also conducted. The results of this mixed methods study showed that assistants, teachers and parents have a tendency to evaluate their collaboration more positively after assistants have made use of an online tool for professionalisation. All of them perceived the regular exchange of information to be particularly important. The results of this study also showed that clear definition of the roles and responsibilities of assistants is necessary if they are to work successfully in schools.