Do the students that report "friendly" teachers perform better on standardized tests? I'll preface this by saying that I've been considering this question in light of the "Summer of Love" initiative and subsequent blog posts, which are looking at the extent to which comments are "friendly" on Stack Exchange.

Much of the impetus behind the movement is a commitment to treating new members better, and it's safe to assume that a majority of these new members are here for help in the process of learning something (e.g., programming, statistics, new software).  Comments can both set the tone while also being a means through which to deliver learning.

The actual Stack Exchange study is measuring the response of a third party to the comments made on the site, but, as more readily available system, I'd like to find out if a teacher who projects a "friendly" attitude positively affects the learning process.  Conversely, it's not ideal if a teacher uses "unorthodox" methods to motivate students (e.g., sarcasm), but controlling for all other factors, could these methods actually motivate some students to learn better?

While the analogy between educators, students, and Stack Exchange participants is far from perfect, is there support in the educational psychology literature for the notion that teachers reported by students as "friendlier" (on average) help those students achieve higher levels of performance on standardized tests and other evaluations?
I am answering this in parts, as an overview for issues relating to learning outcomes and perceived teacher friendliness. 

To assist, I would categorise friendliness to mean encouragement and rapport (respect may or may not be correlated within this).

Firstly to address integrating theories of teaching and learning.


  Theories of learning and theories of teaching often originate and
  operate independently from one another. This article attempts to
  contribute to the integration of the two types of theories. First, the
  cognitive, affective and regulative activities students use to learn
  are analyzed. Next, different ways in which teachers can regulate the
  learning and thinking activities of students are discussed, as well as
  the teaching strategies they can use for that aim. The third part
  focuses on different ways in which student-regulation and
  teacher-regulation of learning act upon one another. Congruence and
  friction between these modes of control are discussed. From this
  interplay implications are derived for process-oriented teaching,
  aimed at promoting congruence and constructive friction, avoiding
  destructive friction and reducing the gap between learning and
  teaching. 1


Secondly a study that shows the  beneficial and cyclic effect of an encouraging teacher/student relationship. (note the reverse is true for students caught within a negative   cycle)


  On the basis of a new model of motivation, the authors examined the
  effects of 3 dimensions of teacher (n = 14) behavior (involvement,
  structure, and autonomy support) on 144 children's (Grades 3–5)
  behavioral and emotional engagement across a school year.
  Correlational and path analyses revealed that teacher involvement was
  central to children's experiences in the classroom and that teacher
  provision of both autonomy support and optimal structure predicted
  children's motivation across the school year. Reciprocal effects of
  student motivation on teacher behavior were also found. Students who
  showed higher initial behavioral engagement received subsequently more
  of all 3 teacher behaviors. These findings suggest that students who
  are behaviorally disengaged receive teacher responses that should
  further undermine their motivation. The importance of the
  student–teacher relationship, especially interpersonal involvement, in
  optimizing student motivation is highlighted. (PsycINFO Database
  Record (c) 2012 APA, all rights reserved) 2


This study examines the effects of positive versus negative verbal reinforcement on different personality types. It would appear that not all people perform best within the cycle of "friendliness".


  However, there was a highly significant interaction between these
  variables; extraverts performed better under positive than negative
  reinforcement, whilst introverts performed better under negative than
  positive reinforcement. 3


Which brings me to my last point, which is that motivation appears to be improved by a balance between friendliness creating a tension within the classroom.  It also shows that both positive and negative reinforcement are necessary.  


  Motivation
  • Set a feeling or tone for the lesson. Instructors should try to
  establish a friendly, open atmosphere  that shows the participants
  they will help them learn.
  • Set an appropriate level of concern. The
  level of tension must be adjusted to meet the level of  importance of
  the objective. If the material has a high level of importance, a
  higher level of  tension/stress should be established in the class.
  However, people learn best under low to moderate  stress; if the
  stress is too high, it becomes a barrier to learning. 
  
  Reinforcement
  • Positive reinforcement is normally used by instructors who are
  teaching participants new skills. As  the name implies, positive
  reinforcement is "good" and reinforces "good" (or positive) behavior.
  • Negative reinforcement is the contingent removal of a noxious
  stimulus that tends to increase the  behavior. The contingent
  presentation of a noxious stimulus that tends to decrease a behavior
  is  called Punishment. Reinforcing a behavior will never lead to
  extinction of that behavior by  definition. Punishment and Time Out
  lead to extinction of a particular behavior, but positive or  negative
  reinforcement of that behavior never will 4


In conclusion
From the available studies, an underlying friendliness, which enables approachability b students, facilitates learning, but a certain level of discipline and the boundary creating an unequal relationship is also necessary. Suggesting that balance is the key and there are no hard and fast rules, as people have varying learning styles.

1 Congruence and friction between learning and teaching
Jan D Vermunt, Nico Verloop
Leiden University, ICLON — Graduate School of Education, P.O. Box 9555, 2300 RB Leiden, The Netherlands
http://dx.doi.org/10.1016/S0959-4752(98)00028-0, How to Cite or Link Using DOI
Permissions &amp; Reprints

 2 Motivation in the classroom: Reciprocal effects of teacher behavior and student engagement across the school year.
Skinner, Ellen A.; Belmont, Michael J.
Journal of Educational Psychology, Vol 85(4), Dec 1993, 571-581. doi: 10.1037/0022-0663.85.4.571

 3 Effects of positive and negative verbal reinforcement on performance as a function of extraversion-introversion: Some tests of Gray's theory
John Boddy, Annabel Carver, Kevin Rowley
Department of Psychology, University of Manchester, Oxford Road, Manchester M13 9PL, England
http://dx.doi.org/10.1016/0191-8869(86)90111-X, How to Cite or Link Using DOI
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 4 Carrie Ekey, Literacy Coaches Training, Feb. 2012  PRINCIPLES OF ADULT LEARNING By Stephen LiebSenior Technical Writer and Planner, Arizona Department of Health Servicesand part-time Instructor, South Mountain Community Collegefrom VISION, Fall 1991