DP,

The typical progression for a student at most programs is:

Private Pilot
Instrument Pilot
Commercial Pilot Single Engine
Commercial Pilot Multi Engine
Flight Instructor
Flight Instructor Instrument
Flight Instructor Multi Engine

However depending on ones needs and the flexibility of the program, some students might do the Multi Engine before the single engine commercial, or do all of the Multi Engine stuff all in one block after they do the single engine stuff up through CFII.