Vicki Zack, a classroom teacher and researcher, returned to the fifth grade classroom in 1989 after more than a decade of teaching in a university faculty of education in order to teach in the changing ecologies of classrooms (with problem-solving approaches in mathematics and literature-based approaches in reading) and to research from the "inside". Since 1996, Zach and David Reid have worked together on various aspects of the children's notions of proving and convincing. In this, the first of two parts, the authors first talk about some of Margaret Mackey's thinking about the idea of "good enough", detailing some of Mackey's thinking and that of others whose thoughts have contributed to their working definition of "good enough". The authors provide a little background about themselves so that readers will know how this collaborative research arose and evolved. Finally they offer two examples of how students operate with good-enough understanding, further building on ideas gleaned from Mackey's article and those of other authors.