<p>Although both family risk and school connectedness independently predict suicidal ideation, the extent to which school connectedness mitigates adolescent suicidal ideation in the presence of deprivation- and/or threat-related family risk remains unclear. Participants were 1227 Chinese adolescents (<i>M</i>_age = 15.67, <i>SD</i> = 1.03; 48.2% female; 57.5% 10th graders, 42.5% 11th graders). Three-wave longitudinal data on family risk, school connectedness, and suicidal ideation were collected with a three-month interval between each time point. Growth mixture modeling and multinominal logistic regression were conducted to extract suicidal ideation trajectories and identify associated antecedents. Analyses yielded four subgroups: low-stable, moderate-quickly increasing, high-slightly decreasing, and high-quickly decreasing. Setting the low-stable as the reference, deprivation significantly increased the probability of belonging to high-quickly decreasing; threat (low family cohesion) increased the probability of belonging to moderate-quickly increasing; and threat (family conflict) increased the probability of belonging to high-slightly decreasing. Family conflict also predicted higher probability of belonging to high-slightly decreasing when pairs of high-risk trajectories were compared (i.e., decreasing trajectories versus moderate-quickly increasing, high-quickly decreasing versus high-slightly decreasing). School connectedness decreased the probability of belonging to high-slightly decreasing in the presence of family conflict; but it did not decrease the probability of belonging to other trajectories in the presence of deprivation or lack family cohesion. Findings suggest suicide prevention should consider family risk and social ties and their clinical functions on suicidal ideation.</p>