The current study examines the performance and achievement of students in the Systematic Qualitative Analyses of Cations (SQACs). We sought answers to questions such as, ‘What are the students’ levels of performance?’ and ‘What is the relation between the average scores for performance and achievement?’. This was done by using the I diagram as a tool within a Guided Inquiry Learning Approach (GILA), which is based on the constructivist theory. The sample consisted of sophomore students (N = 31) taking the Analytical Chemistry Laboratory-I course and attending the Chemistry Teaching Program of the Faculty of Education of a state university in the Aegean region of Turkey. During the analyses, the students attempted to solve specific problems and find the results of their qualitative analyses as they followed the sections of I diagram step by step under the guidance of researchers. They also tried to find solutions to problems through logical reasoning and discussions with each other. A positive correlation was found between the achievement and performance of the students. During the experimental process based on the GILA, the students were able to structure their knowledge more clearly by carrying out cation analysis in a systematic manner, inquiring and suggesting scientific explanations. Although they had difficulties in some sections of the I diagram, including logical argument, data transformation and variable definition, they were able to establish a link between theory and practice by using their cognitive and meta-cognitive skills.