This paper describes the development of the BE COOL! learning environment that gives all children, gifted and non-gifted, the opportunity to learn at a level matching their specific needs and abilities within the social context of regular education. BE COOL! uses the ability-adjusted jigsaw method, in which children of varying ability levels work together on a design for which they acquire knowledge by working on tailored assignments in groups with children with the same ability level. This differentiation method unites elements of learning by design, learning together, and learning by inquiry. In this article, we first present the conceptual foundations underlying BE COOL! Next, we describe the learning environment and its components as incorporated in a seven-week science lesson series in which fourth to sixth graders must design a liveable house on the moon for a family of four. Then, we describe our design process, in which research and development alternated and we end with a brief presentation of the learning environment's added value for educational practice.