Background: The incidence of first suicidal thoughts and behaviors (STBs) peaks during early adolescence. After experiencing their first STBs, adolescents differ greatly in the extent to which they continue to have STBs. Aim: We determined the course of STBs in Dutch students at two ages: 13–14 years (t1) and 15–16 years (t2). Methods: Longitudinal data on STBs and sociodemographic factors were collected by self-report (n = 8,499). Associations between having STBs at t1 and t2 were determined with multinomial logistic regression analysis. Results: Students who reported suicidal thoughts at baseline (n = 1,077; 13%) reported suicidal thoughts (OR = 6.60; 95% CI [5.52, 7.88]) and suicidal attempts (OR = 6.97; 95% CI [4.20, 11.54]) at t2 more often than students with no STBs at t1. Students who reported a suicidal attempt at baseline (n = 144; 2%) also reported suicidal thoughts and suicidal attempts more often at t2 (OR = 5.98; 95% CI [3.89, 9.21]; OR = 30.00; 95% CI [15.84, 56.82], respectively). Limitations: The use of confidential self-reported data and the loss of cases after merging could have biased the results. Conclusion: For a subgroup of adolescents, STBs persisted and worsened over the 2 years. This demonstrates the importance of accurate identification of those at increased risk of suicide, in combination with personalized care.