Background: Clinical teaching competencies are a core requirement for nursing educators, contributing toward better nursing student achievement in clinical settings. The study aimed to assess training program for improving nursing educators' clinical teaching competencies and its effect on nursing student achievement. Study design: A quasi-experimental design was utilized. Setting: The study was conducted in Secondary Technical Nursing Schools associated with the Directorate of Health Affairs in Menoufia Governorate named "Sers Elyan, Menof, Elbagour, Ashmon, and Shibin Elkom". Study subjects: 60 all available nursing educators and130 undergraduate nursing students from the five selected Secondary Technical Nursing Schools from 2nd and 3rd academic year (2021-2022) who were selected using proportion allocation sampling 30% from the total number of nursing students Tools of data collection: Three tools were used; Tool (1) Clinical teaching competencies knowledge questionnaire, Tool (2) Observational checklist for clinical teaching competencies, Tool (3) Observational checklist for nursing students' achievement. Results: There was highly statistical improvement in nursing educators knowledge and performance regarding clinical teaching competencies (78.3% & 95.0%) and (75.0% & 90.0%), respectively at the immediate post and follow-up phases of the training program, as well as the majority (88.5%) and about three quarters (74.6%) of the studied nursing students had good clinical evaluation achievement at the immediate post and follow-up phases compared with 7.0% of them at the pre-training program. Conclusion: There was a highly statistically significant positive correlation between total knowledge, performance regarding clinical teaching competencies, and nursing students' clinical evaluation achievement at immediate post-training program phases. Also, there was a statistically significant positive correlation between total knowledge, performance regarding clinical teaching competencies, and nursing students' clinical evaluation achievement at follow-up phases. Recommendations: Establishing an orientation program for the preparation of new nursing educators about the principles and evidence-based practice of clinical teaching competencies that effects on nursing students' achievement.