Taking exams is one of the best ways to become a great musician.  They give students UCAS points from Grade 6 to 8 helping them get into University, they create discipline by making them improve all areas of guitar and musicianship.  They are also a great way of learning to perform with confidence and correct technique. 
Exam boards:
RGT@LCM - Acoustic Guitar, Electric Guitar, Ukulele, and Bass,  
LCM - Classical Guitar only, Luke does not approve ABRSM guitar exams.
RSL - Electric Guitar, Acoustic Guitar, Bass Guitar, Ukulele, These exams are harder than RGT and require serious dedication, however they cover the same criteria, therefore the end result is the same.    

RGT Exams

To enter an RGT@LCM exam head over to: rgt.org 
Select: Enter an exam, then Register for a new account (or sign in if you've entered before), follow the instructions from there.

LCM Classical Guitar Exams

Head over to: eric.uwl.ac.uk 
Select: register, then follow the instructions from there.

RSL

Head over to: rslawards.com
Select Rockschool, then hit enter online, choose 'I'm a new customer' and follow the instructions. 

Any issues with dates or times please call them and not Luke :)