This study examined the bidirectional, longitudinal relationship between loneliness and affective peer status (positive and negative) during the transition from late childhood to early adolescence, also focusing on potential sex differences in these dynamics. Using data from a representative sample of 4,462 Polish students ( Mage = 9.9, SD = 0.33; 51.0% girls at Wave 1), a two-wave cross-lagged panel model was applied to assess these associations over 1.5 years. The results confirmed the hypothesis of a reciprocal relationship between loneliness and peer status over time: A higher level of loneliness predicted lower positive peer status and higher negative peer status, and vice versa. In turn, the findings challenged the asymmetry hypothesis, which posits that negative peer status is more strongly associated with loneliness than positive peer status, indicating instead that both types of peer status predict loneliness to a similar extent. However, sex differences emerged: Loneliness in girls was more strongly linked to positive peer status, while boys’ loneliness was more affected by negative peer status. Moreover, negative peer status demonstrated greater stability over time compared with positive peer status. This study supported the reciprocal nature of loneliness and peer status, highlighting their dynamic interplay rather than a unidirectional effect. Additionally, while the asymmetry hypothesis was not supported, it was observed that the effects may differ between sexes. Therefore, future research should refine theoretical models by considering sex-specific patterns and their implications for interventions aimed at improving peer relationships and reducing loneliness during the transition into early adolescence.