The study investigates mathematics lesson plans that teachers produced for re-teaching purposes. Its goal is to determine which aspects of mathematics-content knowledge are expressed in lesson plans on the topic of fractions prepared by primary math teachers and intended for underachieving students, and to see how these aspects are manifested. The data were gathered in an analysis of forty-nine lesson plans that the participating teachers prepared. The data were analysed in two phases: (1) a category analysis of the plans and (2) a statistical analysis of the data obtained, via cluster analysis and ANOVA tests. The findings point to four types of teachers in terms of their mathematical knowledge: (1) those whose knowledge is faulty; (2) those who have incomplete or scanty understanding of math but know how to phrase a mathematical idea correctly; (3) those who understand mathematical content well but are not strict about correctly describing the "mathematics" that they teach in the lesson; and (4) those thoroughly versed in mathematics, from whose lesson plans one may infer both correct wording of the mathematical idea and consistently correct use of mathematical concepts and principles. Despite the differences in their content knowledge, teachers of all four types planned to teach their students at a procedural level while attempting to impart conceptual knowledge--most likely because they expect little of their underachieving students. Practical recommendations derived from the study are offered.