Missing Prefects

[brwneil]

No: HPFGUIDX 135715

Could someone please explain how the prefect system works.  In book 
five Ron and Hermione get made prefects and it seems they are the 
only two in Gryffindor.  They patrol the train, lead the first years 
to the dorm and it is only Hermione who takes on Fred and George.  I 
thought at the time that being a prefect was only for one year. 

Now we are in year six and still they are the only prefects in 
Gryffindor that we hear of.  Hermione again sees to the first years, 
but there is no reference to anyone helping her.  

Are we to assume that last year the sixth year prefects didn't do 
their job and that this year the fifth year prefects are also not 
performing their duties?

I understand that these missing prefects are not important to the 
story line, but they are treated more like being nonexistant than 
missing.

Obviously neither Luna or Ginny made Prefect for their year because 
neither had to go off with Ron and Hermione.  Molly wasn't even 
disappointed at Ginny not making it.  It seems that HBP was quite 
rushed and very much information left out of the book.

Neil