The teaching of mathematics, even in the selective private schools in Pakistan, is done in a traditional fashion. This kind of teaching helps students follow pre-ordained rules, transmitted by the teacher, without understanding the rationales for them. The consequence is that students develop proficiency in procedural skills but lack reasoning and thinking capacity in mathematics. This study was designed to investigate how a small sample of upper primary school students could be helped to develop a relational understanding of some basic number concepts. Using an action-research approach these students were engaged in a set of mathematical activities which allowed the researcher to trace their thinking. Data collection in this study occurred in three stages. At the Pre-Intervention stage semi-structured interviews and classroom observations were conducted to ascertain how students learned and were taught mathematics in their school context. During the Intervention stage the researcher set students various mathematical activities to help trace their mathematical thinking and learning. At the Post-Intervention stage students discussed in small groups both, the helping and the constraining factors in developing their relational understanding in mathematics. The findings that emerged were that multiple representations, the appropriate use of mathematical language and students' efforts to justify their claims helped them learn to reason mathematically. However, the teacher's own inadequacies in mathematical concepts and the limitations of words and pictures in representing abstract mathematical ideas sometimes constrained what the students could learn.