Teacher Immediacy

Effect Size d = 0.16  (Hattie's Rank = 115). Note in the latest rankings (Jan 2019) from Visible Learningplus a general category of Teacher Attributes seems to have replaced Teacher Immediacy.

One meta-analysis was used:
Allen, M., Witt, P., & Wheeless, L., (2006). The Role of Teacher Immediacy as a Motivational Factor in Student Learning. Communication Education, 55(1), 21-31.

The author's state the theoretical model,
"...posits that teacher immediacy, a behavior perceived by students, generates increased involvement and enthusiasm for the material and the instruction. Mehrabian (1969, 1981) viewed immediacy as a set of behaviors creating a perception of physical or psychological closeness between communicators. Using immediacy behaviors bridges the psychological distance between the two persons" (p. 21).
The authors further explain that,  
"The efficacy of nonverbal immediacy behavior is based in a reinforcement paradigm underlying attraction theory (Mehrabian, 1981). Stated simply, persons approach those stimuli that provide rewards and are passive or avoid those stimuli that are not rewarding or punishing. Immediacy behaviors that a teacher displays in communicative acts and interactions with students, therefore, can be seen as rewarding. It follows that these rewarding behaviors may serve as reinforcement for the attentive behavior, feedback, and interaction from the student that increase affective, cognitive, and behavioral learning" (p. 22).
The research completed was on college students over 4 years and was not a true experiment but another correlation study. In fact, it was a number of different correlation studies. 

Note, many scholars have asked Hattie to remove studies on university students as they do not represent school age students.

Their summary shows 2 correlations:
1. Teacher Immediacy and Affective Learning (attitude, motivation, etc.) and 2. Affective Learning and Cognitive Learning (recall, understanding, etc.) (p. 26).

They summarise the 3rd correlation between all measures of immediacy (verbal, nonverbal, and combined) and cognitive learning is estimated, r = 0.13 (p. 24).

Also, they report (p. 29) nonverbal immediacy to cognitive learning r = 0.17

However, Hattie uses the lower value r = 0.08 to derive his effect size d = 0.16. 

But he should have used the 3rd correlation of r = 0.13 he would have got d = 0.26. He could have also reported the higher correlation of r = 0.17 and d = 0.35.

In any case, using correlation in place of a true experiment to derive an effect size is not very reliable. See Correlation which goes into detail how correlation is converted to an effect size and the major problems with this.

The authors also state the limitations of the study (p. 27),
"These findings should be interpreted with caution, given the limitations of the analysis. The data pool remains fairly limited and the model analyzed relatively simple. More sophisticated thinking should be developed concerning the effects of immediacy behaviors, improved affect, and cognitive learning."
Hattie's low effect size place this in his "going backwards", also-ran" and "disaster" categories - see Hattie's 2005 ACER Lecture.

However, in light of Hattie's new mantra - the story, the story, the story ...  the authors give a different story (p. 28),
"The research outcome in this report continues to justify attention to teacher immediacy as an aspect of classroom behavior that can improve learning outcomes by increasing student motivation. Motivation for students is not unimportant, with college dropout rates exceeding 50% (Ehrenberg & Zhang, 2004); the actions that an instructor can take to reduce that attrition are not unimportant. The impact on education may not be as direct as what is learned in a particular class. If the motivation to finish the degree or the program of study is improved, the higher graduation rates may occur."
They continue and question Hattie's entire model of a single focus on student achievement (p. 29),
"The problem is that often the outcomes or assessment imply evaluations reflecting a rather limited view of the purposes of educational practices. An educational practice that is effective at creating ‘‘learning’’ but increases the long-term dropout rate provides only a short-term questionable benefit that may or may not really be in the best interests of the system. The real view of assessment or evaluation of educational effectiveness should probably take a broader view of the educational system and consider both the immediate local needs of a course and the long-term goals of the process of education... 
Such an assessment requires an entire body of longitudinal research focusing more on systemic interests about educational outcomes. The tendency of educational research... is to focus on a point in time for the instructor and the course. The real measure of success for the institution should involve how well and whether the student completes the course of study."