Skyhawk 172/Cutlass 172
Flight Crew Commercial; Flight Crew Multiengine
Flight Crew Last 90 Days 40; Flight Crew Total 300
Communication Breakdown; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance
Human Factors
Another instrument rated pilot along with me; on an IFR flight plan under my name made a deviation of altitude and heading. Socal called and brought [the deviations] to my attention.  I corrected immediately.
The C-172 pilot of record on an IFR flight plan failed to note his assistant pilot's course and altitude deviations until advised by ATC.