This study used a cross-lagged panel analysis to explore the effect of impulsivity and academic achievement on the development of suicidal ideation in adolescents using three-time assessments with an interval of 6 months. A total of 211 adolescents (104 boys, 107 girls with a mean age of 13.62 ± 0.68 years in the third assessment) completed the Barratt Impulsivity Scale, the Monthly Exam, and the Suicidal Ideation/Suicidal Attempt Questionnaire to evaluate the level of impulsivity, academic achievement, and suicidal ideation, respectively. Our results showed that impulsivity was a primary risk factor of suicidal ideation in adolescents during their early stage in junior high school, especially for girls, while academic achievement had an increasing effect on suicidal ideation as adolescents progressed to the higher grades in junior high school, suggesting that taking appropriate intervention measures at specific stages might be critical to prevent suicidal ideation in adolescents.