> eight-session DBT skills-training intervention (‘WISE Teens) (n = 563) or class-as-per-usual (n = 508). On average, the ‘WISE Teens’ intervention did not improve outcomes with significant deteriorations or null effects observed across outcomes relative to class-as-per-usual immediately post-intervention. The largest deteriorations were observed for depressive (d = −0.22; 95% CI = −0.35, −0.08) and anxiety symptoms (d = −0.28; 95%CI - = −0.41, −0.14