In many countries in recent decades, great importance has been placed on the concept of quality assurance in education. In Slovenian schools, quality assessment and assurance processes are based on a combination of self-evaluation and external evaluation, although significantly more weight has been attached to self-evaluation than external evaluation lately. Efforts to achieve the highest possible levels of quality and school work performance are based on the assumption that the concept of quality should be developed at the level of the professional autonomy of schools and individual teachers. Our empirical research, which was conducted on a sample of 1,530 teachers, counselors, and headteachers of primary and secondary schools in Slovenia, showed that the majority of professional workers in education recognize the importance of conducting self-evaluation for their profession. Using factor analysis, it was established that the frequency of conducting self-evaluation in schools is most affected by the following factors: (a) the opinion of headteachers, teachers, and school counselors on the positive effects of self-evaluation; (b) the school climate; (c) the attitude of headteachers, teachers, and school counselors toward research; and (d) the attitude of headteachers, teachers, and school counselors toward their own professional development. Multiple regression analysis of the obtained factors was made, and a model was designed to predict the frequency of the performance of self-evaluation. It was established that the frequency of conducting self-evaluation is most strongly affected by the attitude of headteachers, teachers, and school counselors toward their own professional development and by their opinions on the positive effects of self-evaluation.