We have developed an educational software tool (Aprendiendo) to reinforce the learning process of children with special educational needs. This tool makes use of a variety of interactive technologies such as Embodied Conversational Agent and multimedia elements (video images from a WebCam, pictures and photos). In this paper we propose a multidisciplinary approach to system design and the evaluation of the users' experience, involving the engineers, teachers therapists and the children themselves, and combining Wizard-of-Oz with other techniques commonly employed in this educational context. We illustrate our approach with a real user evaluation of Aprendiendo's emotions module. Categories and subject descriptors K.4.2. [Computers and society]: Social Issues Assistive technologies for persons with disabilites General Terms Design, Human Factors Keywords Educational software, Reinforcement learning, Embodied conversational agents, Evaluation scheme, Emotions