The effects of the teacher’s expectations on students’ motivation remain an area of investigation where the results are still controversial. This article presents the main results of a study on the relationship between motivation expectations of Physical Education (PE) teachers and the behaviors exhibited toward their students in a natural context of PE teaching in Tunisia (gymnastics cycle). The theoretical framework is based on three categories of work: 1) the work on the “Pygmalion effect”, 2) research relating to self-determination theory and classroom interactions expressed by quantity, content and the style of verbal communication between teachers and students, and 3) the work examining the links between teachers’ initial expectations towards the students and these interactions. The objective of this study is to analyze the consequences of pre-existing and lightly studied expectations regarding the motivation on the frequency, content and motivational style (i.e., controlling vs. autonomy-supportive) interactions that a PE teacher has with students. Seven hundred and thirty students from all classes of second cycle basic education and their thirty teachers were observed during gymnastics classes. The teachers’ motivation expectations and self-determination index of students were measured at the beginning of the cycle. The teacher-student interactions were recorded during each session (50 minutes) corresponding to a teacher (thirty sessions on the whole) and encoded using two instruments. The main results show that: a) teachers have expressed more communications with high expectations than low ones; b) the teachers’ expectations are positively related to technical instructions and autonomy-supportive style and negatively to unfavorable affective feedback and a controlling style. These different dimensions mentioned above make up important mediators of “Pygmalion effect” that certain studies have noted in PE.