This article describes how the Problem of the Week Environment at the Math Forum online mathematics resource allows K-8 preservice teachers who are enrolled in mathematics content problem solving-classes to experience the process of reading, evaluating, and replying to young problem solvers' work with thoughtful comments and effective hints. This online project includes the training of college-student mentors, the assignment of problems, and the approval of replies. This article focuses on the twofold purpose of the mentoring project: first, to give preservice teachers a special type of field experience by guiding K-8 students to write better solutions via questions and helpful suggestions; and second, to allow preservice teachers the opportunity to reflect upon the variety and richness of approaches generated by a rich mathematical problem.