My experience in teaching rock guitar over the past 10 + years have lead me to conclude that there are a lot of bad teachers out there! Correct technique and knowledge is essential with any instrument, and the way you are taught initially can have a big impact on the speed of you development as a player. This is an area that is particularly neglected by Rock guitar teachers.
Be sure to check potential teachers credentials before commencing lessons, it will save you time and money in the long run!