To prevent colorectal cancer, high-quality colonoscopy is advocated, undertaken by endoscopists with high adenoma detection rates (ADRs). Despite reports that various factors may impact ADRs, the significance of such factors is still unclear. The analysis was aimed at quality-oriented interventions for boosting ADRs. Study enrollees were adults subjected to screening colonoscopy between September 2013 and August 2016 at the Gangnam Center of Seoul National University Hospital Healthcare System. The investigation entailed six periods (P1-6) of 6 months each, during which serial multidirectional quality improvement efforts were instituted. In particular, we sought to further educate endoscopists, provide feedback on individual ADRs, and introduce a split-dose regimen, gauging results via the Boston Bowel Preparation Score. Changes in polyp detection rates (PDRs) and ADRs were then analyzed. A total of 13,430 colonoscopies were undertaken by 15 experienced endoscopists. Overall, the ADR increased from 45.6% (P1) to 48.2% (P6, p < 0.001). The PDR, ADR, and advanced adenoma detection rate (AdvADR) showed the greatest increases between P3 and P4 [PDR 67.8% → 71.2% (p < 0.001); ADR 44.1% → 47.7% (p = 0.001); AdvADR 2.3% → 3.3% (p = 0.028)] in keeping with the introduction of a split-dose regimen. The sessile serrated adenoma detection rate (SSADR) increased substantially from 2.1% (P1) to 7.9% (P6, p < 0.001), with the largest gain between P1 and P2, just after education (p = 0.023). Successful quality improvement in colonoscopy was achieved through comprehensive multidirectional efforts in education, feedback, and enhanced bowel preparation. Achieving high-level bowel preparation was paramount in ADR improvement. The SSADR was improved through education.