Sometimes you would need a referral from your pediatrician, othertimes you may be able to schedule directly so check with your insurance on that.
Typically you would fill out a good deal of advance paperwork so the diagnostician can get a feel for where to go with the process. Sometimes forms will also be sent to teachers to fill out.
First appointments often are with parents only--no children. Ditto with the follow-up after all the testing is finished to go over the findings and recommendations. What happens in between there depends on the age of the child and what kind of testing the np feels is needed, but usually ranges from about 5-14 hours of testing. Sometimes referals are made to other specialists based on the findings.
http://www.conductdisorders.com/forum/showthread.php?t=337