When final year medical students reporting poor prescribing confidence were tested, key prescribing weaknesses emerged. This study aimed to characterize student variability in both the experience of and cognitive levels displayed during prescribing. Blooms Taxonomy cognitive categories were assigned to each question of a student test measuring prescribing ability. For the true/false questions, students scored highest within the lowest two cognitive categories. Results were lower for mid-ranging abilities and were lowest for the highest ranking category, "evaluation". For short-answer questions, the lowest and highest ranked cognitive categories produced the best (36.9%) and worst (16.6%) average results respectively. The qualitative data, gathered from student interviews with paper case treatment decisions, revealed prescribing reasoning predominating at different Bloom levels. Phenomenographic analysis exposed different shifts in prescribing conceptions, developing from the mechanistic use of medicines to considering the patient more holistically. This understanding will assist the guiding of students toward more mature prescribing conceptions. (Contains 7 tables.)