Teacher reflection is becoming increasingly important in cultivating a responsible, critical, and autonomous work of teachers in practice. Little research has been conducted in Serbia, and these are predominantly theoretical. There is no validation of metric tools that could be applied in researching teacher reflection. The aim of the research illustrated in the present paper is to determine to construct validation of the factor structure of the English Language Teaching Reflective Inventory(ELTRI) within the Serbian educational context among primary school teachers. The research included 310 teachers of upper-primary subjects and elementary school grade teachers. We have applied exploratory factor analysis and extracted variables and determined four factors: affective, metacognitive, cognitive, and practical elements of teacher reflection. The reliability of the first three subscales (affective, metacognitive, and cognitive) was satisfactory, while the reliability of the fourth subscale (practical element of teacher reflection) proved to be low in our research. This is possibly caused by the research sample and education context of the respondents. The conclusion is that, in our sample, Teaching Reflective Inventory (ELTRI) can be used in a reduced form when testing teacher reflection, with 23 items and three factors. The present paper also gives the authors’ recommendation of adding the practical element factor with an appropriate number of items which potentially obtain a four-factor solution to the questionnaire.