When a resident performs a minor surgical procedure, the attending physician must be present for the entire procedure, in order to bill for the service under the attending physician's provider number.

Minor surgical procedures performed by medical students are never billable to Medicare or any third party. 

Medicare defines these procedures as those that take less than five minutes to complete.

Who needs to document the service, and the teaching surgeon's presence?  The Medicare Claims Processing Manual does not indicate that.  Unlike in other sections, in which the manual specifically states what the attending must document, there are no specific requirements listed.  As such, many teaching facilities allow the resident or nurse to document the attending's presence.  Although this is not specifically supported by the manual, it seems reasonable given that the manual does not mandate that the attending document their presence and that the attending does not need to personally provide any of the care.

What might that look like?  The resident would describe the indication, consent, procedure and follow up instructions, and then add, "Dr. Thomas was in the room for the entire procedure."

From the Medicare Claims Processing Manual (Publication 100-04, Chapter 12, Section 100.1.2 A3

3. Minor Procedures
For procedures that take only a few minutes (five minutes or less) to complete, e.g.,
simple suture, and involve relatively little decision making once the need for the
operation is determined, the teaching surgeon must be present for the entire procedure in
order to bill for the procedure.