This study investigates the relationship between the students' understanding of the aims of an investigative activity and their performance when conducting it. One hundred and eighty-one year nine students from a public middle school in Brazil took part in the study. Students working in pairs were asked to investigate two problems using a computer-based environment. All their attempts to collect information were recorded in a log file, which registered the history of each duo investigation. After completing each investigation, all the participants were asked to explain in writing what the objective of the task was. Results obtained showed that a proportion of the students had some difficulties recalling the declared aims of the activities. However, those who succeeded in recognising the stated aims of the tasks showed a superior performance in conducting their investigations. This performance was graded according to both the proportion of adequate and consistent tests carried out and the quality of the investigation which was done. (Contains 17 tables and 3 figures.) [Funding for this article was provided by the CNPq.]