Background: Adolescents are the most affected group and the group that is least studied when it comes to malnutrition, which is one of the most important public health concerns in underdeveloped countries, including Ethiopia. Therefore, the goal of this study was to assess nutritional status and related factors among teenage females who are in school. Materials and Methods: From October 1 to October 25, 2018, 645 young girls in school participated in an institution-based cross-sectional study. Girls in their teen years from the school were selected using a simple random sample method. Anthropometric tests and in-person interviews were used to collect the data. An odds ratio with 95% confidence intervals (CIs) and a p -value under 0.05 were used to declare a statistical association. Results: This study found that 12.3% and 9.6% of school adolescent girls were stunted and thin, respectively. Being a rural resident (adjusted odd ratio [AOR]: 1.85, 95% CI: 1.05–3.28) and inadequate dietary diversity score (AOR: 3.02, 95% CI: 1.06–4.60) were significant predictors of stunting. School adolescent girls from merchant father were 71% less likely to develop stunting compared with government employee father. Late adolescent age (AOR: 2.27, 95% CI: 1.28–4.02) and family size ≥5 (AOR: 1.98, 95% CI: 1.05–3.75) were significant predictors of thinness. Conclusions: Stunting and thinness were the major public health problems among school adolescent girls in the study area. Being a rural resident and inadequate dietary diversity increases the risk of stunting. However, being late adolescent girl and large family size were risk factors for thinness. There was a need for a school-based instruction program that concentrated on a varied diet and methods of encouraging the adolescent girls' appetites.