Part of this was my fault.  I didn’t explain factors clearly enough when I taught the lesson so I felt like I was playing catch up from then on.  The best way to clarify the difference was with a flow chart showing where explanatory variable, factor, level and treatment all lie in relation to each other.

Explain how there should be another researcher who would know who received what treatment.  However, even if there was not, the researcher could cover the pill bottles and mix them up.  Then they could dispense treatment and uncover the bottles later to see which group had each treatment.