Background. Child undernourishment is the disturbance of body function arising from a dietary imbalance between body demand and supply, which is the most serious public health problem in developing countries. Objective. This study aimed to assess the magnitude of nutritional status and associated factors among full-cycle primary schoolchildren in pastoral communities in the Mieso-Mulu district, Sitti Zone, Somali Regional State of Ethiopia. Methods. An institution-based cross-sectional study design was used. Study participants were selected using two-stage sampling procedures. Data were collected using structured, translated, pretested, and interviewer-administered questionnaires. The weight and height were measured using a calibrated digital scale and a Seca Rod stadiometer, respectively. Microscopic identification of intestinal parasites was done. Multicollinearity was checked for independent variables. Height for age z scores (HAZ) and body mass index for age z scores (BAZ) were used to determine the nutritional status of children. Logistic regression with both bivariate analysis and multivariate analysis was applied to identify associated factors with the nutritional status of children. Adjusted odds ratios were reported and the level of statistical significance was declared at a P value <0.05. Results. The magnitudes of thinness and stunting were 13.1% [95% CI: 10.6%, 15.7%] and 24.6% [95% CI: 21.3%, 27.9%], respectively. Being male, not using a bed net, and the presence of intestinal parasitic infection were among the factors associated with thinness. Family size of less than five, household food insecurity, and unavailability of the latrine were among the factors associated with stunting. Conclusion. This study revealed that stunting and thinness are major health problems among schoolchildren. Household food insecurity, intestinal parasitic infection, bed net utilization, and the availability of latrine were some of the major factors significantly associated with undernutrition. Local policymakers, health programmers, nutritionists, health practitioners, and nongovernmental organizations should enhance the nutritional status of schoolchildren by using information dissemination interventions, particularly in improving waste disposal, sanitation/hygiene, latrine facilities, and school-based deworming. Furthermore, awareness creation using nutrition promotion and encouraging communities to attempt to diversify locally available and low-cost nutritionally effective food items to improve food consumption and distribution within a household is recommended to reduce the prevalence of undernutrition among schoolchildren.