Change of Custody - NC - Does this meet guidelines?

[peterson2008]

Long story short, 12 yo son of my husband - shared custody with visitation since 2005.  Mother is custodial caregiver.  She moved without notice, dad had to track her down, refused visitations, withheld medical, school, etc information from ex.  Fast forward 2007, mother found in contempt of court due to above.  Jail sentence suspended if she made up missed visitation, ensures dad can have regular contact, provides information on son's health (nothing serious, dad just never knew son was sick)

2008 - over past three years son's grades have gone into the toilet. He refuses to do homework, disruptive in class.  Mom (have school documentation) says there are 'problems at home' that keep him distracted.  Father has asked both what the problems are, mom refuses to answer, son says nothing is going on.  

Son almost (by two points) fails 7th grade, but aces all his tests.  Appears very bright, just not keeping up with homework. Very bright kid, bored to tears in math and science.  Hates school. Mom does not manage homework or  school activities.

Son has not seen a dentist in three years, has eye teeth growing over existing ones, mom will not make a dental appt.  

Phone calls to son on regular Tues nites (as ordered by court order) don't get answered regularly, Father gets no information on school, health, etc from Mom and has to chase it all down through schools, doctors, etc.

We want to ask for a change in custody and have the son live with Dad and I.  We are married, have better incomes, live in an area where the schools are significantly better (state documents of school performance shows this) and are wondering how to start.  

We've been told that we should write to the Mother, making a proposal for son to live with Dad over the summer so that he can participate in a study program to get his study skills, grades up, and get him some seriously needed dental attention.  Then if she refuses, take it to court.

Thoughts, suggestions, or advice would be greatly appreciated.  

Thank you all.