Does the way instructions for carrying out elementary operations are presented affect the time required to complete those procedures, student’s critical thinking ability, and student’s final grade? This investigation sought answers by presenting prescriptions — or algorithms — in three ways to university students in an introductory laboratory-chemistry course. Differences in the effects of the three representation modes — flow charts, lists, and standard prose — were complex and changed over the 10 lab sessions. There was no evidence that representation mode affected either critical thinking ability or final grade.