Background/Objectives: The discrepancy between the current perceived body image (BI) and beauty ideals leads to dissatisfaction, which is believed to be common among adolescents. This study aimed to investigate the stability in BI perceptions and dissatisfaction during early adolescence. Another aim was to highlight differences in dissatisfaction according to Body Mass Index (BMI) and inconsistencies in weight status perception. Methods: Two hundred and nine participants (mean age at first survey: 11.33 ± 0.38 years) were enrolled in this longitudinal study with three years of follow-up. Data on size and BI perceptions were collected through individual interviews. Stature and weight were directly measured. Results: Findings indicated significant changes over three years in anthropometric traits but not in weight status prevalence or BI perception and dissatisfaction, except for the ideal figure in males and weight control in females. The results also indicated a significant difference in BI perception and dissatisfaction by BMI categories. Self-reported body measurements were found to be unreliable with a weak-to-moderate agreement between self-perceived and actual weight status. Conclusions: BI perception appears quite stable across the three years considered. Dissatisfaction is similar in both genders, although a tendency toward different gender aesthetic ideals is already appreciable in early adolescence. We suggest that the lower frequency of normal-weight adolescents compared with peers in previous studies is attributable to the effects of the recent pandemic. Given the growing dissatisfaction with increasing BMI and misinterpretations of weight status, school actions to promote a healthy lifestyle and positive BI should be undertaken.