The educational practice of primary school students carrying out research projects has been well entrenched in Australia and overseas for more than forty years, however there is a paucity of empirical studies into what students actually learn from doing projects. Over the past decade some educators have highlighted the problems and possibilities in the use of this instructional method and its demands on the child learner. This thesis is based on the premise that research project work is a complex problem solving task which imposes a heavy cognitive load. Teachers need to structure the teaching/learning task taking into account the nature of learning and the learner to achieve desired learning outcomes by students. Cognitive load theory (Sweller, 1988; 1989; 1993) suggests that many conventional methods of instruction are not effective because they deploy cognitive resources away from activities relevant to learning imposing a heavy extraneous cognitive load. The conventional project method, it is suggested, is one such method of ineffective instruction. The cognitive load needs to be reduced to enable the child researcher to successfully complete the task. A structured approach is suggested as a means of reducing cognitive load. This thesis reports the findings of two experiments designed to investigate the learning effectiveness of primary school children's research projects when using a structured as opposed to an unstructured approach. The projects were carried out with children in two Year 3 and two Year 6 classes. The results indicated that there was a significant learning advantage for students doing research projects through a structured rather than an unstructured approach. In light of these results and previous findings, it is suggested that the skills involved in solving complex problems during research, ie. in seeking, processing, critically evaluating and communicating information from source materials, need to be identified and taught to students directly and within the context of project work, if students are to learn effectively when carrying out research projects in primary schools. Suggestions are also made for future research.