The purpose of the research is to examine, according to generalizability theory, a) the consistency between instructor assessments and self-assessments on concept mapping performance of 100 secondary school prospective teachers who attended Pedagogical Formation Certificate Program at Mimar Sinan Fine Arts University in 2014-2015 academic year, b) their severity-leniency behaviors in these assessments, and c) the difficulty levels of the performance criteria used in these assessments. Generalizability study was carried out by creating a p x c x r (p: person, c: criterion, r: rater) pattern obtained through scoring of the designed concept maps by the prospective teachers and instructor on the same assessment form. The following were found out based on the findings, - instructors and prospective teachers exhibited equal severity-leniency in scoring both throughout the assessment criteria and by comparison, - performance criteria were distributed across the different difficulty levels, - there was no consistency between prospective teachers’ self-assessments and the instructor assessments, and – self-assessments of prospective teachers were more positive compared to the instructor assessments.