Background: Several reports indicate that long stay at home for online schools due to the COVID-19 pandemic changed the normal physical activity and body weight of school-age students. Previous studies revealed that almost 50% of school students complained of increased or decreased more than 3 kg of weight due to lower physical activity. This study aims to provide insight about the Body Mass Index (BMI) among school students during COVID-19 pandemic. Methods: A retrospective matched-longitudinal study was conducted in 2022 based on previous data about BMI-for-age percentile in school-age students aged 6 to 18 years. These data were collected the year before and during COVID-19 pandemic (2019-2021). Results: All the included students were Arabic (N = 53,580) and were not diagnosed with chronic illness. The outcomes showed that the overall percentage of students with normal weight was 54%, 56%, and 53% during the 2019-2021 years, respectively. Overweight among students increased during the COVID-19 pandemic years, as almost 10% of the students were overweight in 2019 compared with 12% in 2020 and 2021 years. Besides, obese students also increased in the 2020-2021 period compared with the 2019 year (15-17% vs. 10%). In contrast, underweight trends among students declined, as 26% reported in 2019 compared to 17-18% in 2020 and 2021. Conclusion: There are significant variations in Arabic school-age students regarding their BMI values. Obesity was highly detected among children and adolescents during the COVID-19 pandemic years compared to 2019, while underweight cases declined.