This study investigated perceptions of 56 students in 4 general chemistry labs regarding their understanding of chemical concepts and processes. Conceptual understanding of scientific investigation was the focus. Students using a pre-lab guide for lab preparation were compared with students completing a traditional pre-lab assignment. Data sources included a student survey and interviews. Forty-one percent of students felt their pre-lab materials were helpful, sixty-four percent expressed confidence in their ability to learn chemical concepts and processes, and sixty-eight percent were confident of their ability to conduct chemical investigations. The experimental groups exhibited no significant differences. A significant instructor effect was found. Sixty-two percent of the students instructed by the researcher felt their approach was helpful; twenty-three percent of the adjunct's students were positive about their pre-lab tasks. Five themes emerged from the written student comments: aspects of the course, lab-related issues, instructors, assessment, and affective responses. Analysis of the interviews supported survey findings. Students using the pre-lab guide felt better prepared to conduct experiments and had a clearer understanding of chemical concepts and the scientific process. Contains 26 references. (Author)