Diarrheal disease remains a leading cause of morbidity and mortality among children under five globally, with poor sanitation and hygiene accounting for over 88% of diarrhea and malnutrition burden. In Kenya, diarrhea ranks third in under-five mortality, particularly affecting arid and semi-arid regions. School-Led Total Sanitation (SLTS), adapted from Community-Led Total Sanitation (CLTS), uses pupils as change agents for household hygiene knowledge transfer. However, SLTS effectiveness in addressing diarrhea and malnutrition has not been evaluated in Kenya. This study assessed SLTS effects on diarrheal disease and nutritional outcomes among children aged 5-59 months in Baringo County. A pre- and post-test quasi-experimental design with nonequivalent control groups was employed in Mogotio (intervention) and Baringo South (control) sub-counties. Using multistage sampling, 440 children aged 6-59 months were enrolled. The six-month SLTS intervention included capacity building, school health club formation, triggering activities using Participatory Rural Appraisal tools, Information, Education, and Communication materials distribution, continuous sensitization, and household monitoring. Data were collected at baseline and three months post-intervention using electronic questionnaires and anthropometric measurements. Nutritional status was assessed using WHO Anthro software z-scores for length/height-for-weight (HWZ), and weight-for-age (WAZ) to determine wasting, and underweight prevalence. Chi-square analysis assessed intervention-control differences. Baseline and endline socio-demographic characteristics were comparable between groups. At endline, no significant nutritional outcome differences were observed: wasting prevalence was at 15.0% versus 16.4% ({chi}{superscript 2}=0.155, df=1, p=0.694) while underweight was 12.3% versus 13.6% ({chi}{superscript 2}=0.181, df=1, p=0.670). However, diarrheal disease prevalence significantly reduced in intervention versus control groups: 5.9% versus 13.2% ({chi}{superscript 2}=6.738, df=1, p=0.009), representing a 53% reduction. SLTS intervention showed no significant effect on nutritional outcomes but demonstrated a significant reduction in diarrheal disease among children aged 6-59 months. These findings provide strong evidence for integrating school-based sanitation and hygiene approaches into broader public health strategies addressing diarrheal diseases.