Background <p>Precise periodontal diagnosis is taught and routinely performed during dental school training. The aims of this study were to determine to what extent the measurement values obtained by students during their clinical training years correspond to those of licensed dentists; to assess the distribution of divergent results relative to measurement positions; and to identify sources of error. The study also investigated whether fewer errors are made in accessible areas such as the anterior teeth and vestibular areas in comparison with inaccessible areas. Finally, it investigated the influence of students’ level of experience on measurement accuracy.</p> Materials and methods <p>Data for probing depths in 6858 measurements made by students in comparison with dentists were documented and analyzed statistically. The influence of periodontal pocket depths on measurement accuracy was examined, and it was investigated whether the location of pockets (vestibular/oral, anterior/posterior, quadrant, mesial/medial/distal) influenced measurement divergences.</p> Results <p>There were significant differences (<i>P</i> &lt; 0.001) between the students’ and dentists’ measurements, which were in agreement in 63% of cases. Differences of 1&#xa0;mm were observed in 80% of cases, 2&#xa0;mm in 15.3%, and 3, 4, or 5&#xa0;mm in fewer than 5%. Measurement differences in the last clinical course were significantly the largest (<i>P</i> &lt; 0.01). Accuracy in medial measurement points was significantly better (<i>P</i> &lt; 0.001). Differences in measurement accuracy in the anterior and posterior teeth, as well as on the vestibular and oral surfaces, only became apparent after analysis of subgroups for healthy, mild, and severe cases. Patients with severe cases had significantly smaller measurement differences in both the oral and vestibular areas (<i>P</i> &lt; 0.02). Healthy patients had significantly better measurement values in the posterior region (<i>P</i> = 0.02), and patients with mild conditions had significantly better values in the anterior region (<i>P</i> = 0.03).</p> Conclusions <p>The results of this retrospective examination show that students already achieve a comparatively high level of measurement accuracy, but that differences occur, particularly in the approximal region. Targeted practical training and structured feedback systems could help further improve diagnostic precision, which is particularly important when there is a recall system with changing practitioners.</p>