Children should be included in the design process when developing new technology solutions for child users. Involving children from different age groups as well as diverse socio-economic circumstances in participatory design is an unexplored field. In this article we discuss TitanTutor, an educational technology solution that was designed by such a combination of children using cooperative inquiry (CI). Six children aged nine or ten from a disadvantaged community and nine teenagers from privileged circumstances together designed the web-based application that would be used to provide after-school homework support to young children who lack such support. Two distinct user groups are involved—teenage tutors from privileged educational backgrounds and young tutees who live in circumstances where educational support is limited. Our aim was to investigate how existing participatory design methods such as CI should be implemented to successfully design with these groups. We describe the design-evaluation iterations that produced the TitanTutor system. The results show that designing with a mixed team of children has clear benefits but that there are obstacles that have to be overcome to reach successful design outcomes.