Can they function? My guess is sometimes yes, mostly no.  
However, I don't think most PG/EG children would be able to achieve the level of learning they are capable of, even with a dedicated teacher.
I believe my PG child has one of the best school situations available.  She is in a school for the highly gifted.  They have highly educated and trained teachers.  They have specialists in many of their subjects, etc. etc. etc.
However, even there some children have a need to move faster.  My dd is moved up 2 grades in math.  There is a great difference between HG, EG and PG.  Combine that with the fact that not only are there differenct LOG but different gifts as well and it makes for a complex picture. 
 
We have children who are PG in music, art, math, reading/writing but are only HG in other areas.  Even in her classroom (full of highly gifted children) their needs are vastly different from each other.
I can't see how a regular classroom can be a place where a PG child can get all he/she needs to thrive.  At the very best I think they are getting enough (when they are lucky) not to starve.