Gruen was far from a good drafting teacher. He'd often show up late for class and unwilling to teach important lessons that lead to success in the class. He favored women in his class (I noticed since all his special help was with women). At the end of his class I learned nothing about drafting.
Gruen was an awesome woodwork teacher, always had fun in his class with my friends, still keep in contact with him, he's a great guy ! RUEN !!!
Very knowledgeable in the classes he teaches. Calls a spade a spade.
As far as his teaching skills go, he's quite useless beyond an absolutely basic level. You will be left to teach yourself a lot of the time.