Teachers should not only be regarded as professionals with a large amount of knowledge that they must transmit but are also expected to fulfil other functions and possess other qualities to overcome the teaching challenge. This paper is aimed at designing and validating an instrument to identify preservice teachers’ perceptions about the competencies and capabilities that a good teacher should have. The study sample is made up of 230 university students who are in their teaching training practises and internships in schools. According to the consulted literature, we elaborated a questionnaire composed of 23 items that are subdivided into four dimensions: personal qualities, training, pedagogical aptitude, and interaction. We analysed reliability (Cronbach’s alpha value was 0.924, and, by dimensions, all values were higher than 0.75; the Orion accuracy coefficients by dimensions were all higher than 0.88) and construct validity, obtaining a good quality of the items (with factor loadings above 0.50), after eliminating one of them. We also obtained a high correlation between dimensions; the lowest value is 0.87. We have therefore achieved a final instrument made up of 22 items that helps identify the set of qualities that a good teacher must have and can serve as a guide for the design and planning of their initial and ongoing training.