Background: In the past decade, there has been a significant rise in the amount of an individual subscribing to mobile phone services, and this technology is now widely utilized by teenagers. Aim: this study aimed to examine the effect of mobile phone usage on students' academic achievement in primary and preparatory school children. Method: analytic comparative cross-sectional study was conducted on 400 school children in primary and preparatory private schools in Dakhlia Governorate using a multi-stage stratified cluster sample. Tool: a self-administered questionnaire that covers socio-demographic characteristics details, mobile phone usage habits, and attitudes towards its hazards was utilized. The school achievement was obtained from school records. Data collection lasted from October 2020 to January 2021. Results: showed that 94.3% of the school children were using mobile phones, mostly the smart type, 50.7% used their mobile for one hour or less per day, and 39.8%wre taking mobile phones to school; 61.5% had a positive attitude towards mobile phone use. Higher percentages of those having very good and excellent grades were not taking their phones to school (p=0.007). Using a mobile phone at school has a detrimental effect on grades, and mobile phone use is very common among primary and preparatory schoolchildren. Recommendation: stricter rules regarding the use of mobile phones in the classroom are necessary, along with a focus on promoting their use for educational purposes and the learning process.