**Background:** Early intervention alcohol and drug (AOD) programs for disadvantaged young people have the potential to decrease the need for future intervention, but there is limited research on how young people use these programs or their outcomes. This study uses data from The Street Universities, an Australian outreach youth AOD early intervention program, to describe participation patterns, examine changes in substance use and wellbeing over 90 days, and identify which young people benefit most.
**Methods:** Two datasets were used. The first was a prospective cohort of 95 new attendees (aged 14-24, 55% female) over six months in 2018, measuring retention and engagement via surveys at baseline, 2 months, and 6 months. The second was a routine service clinical dataset from 3,893 clients (aged 12-26, 72% male) who received therapeutic services (counselling, case management, or educational interventions) across three sites from 2014 to 2020. Outcomes were measured using the Severity of Dependence Scale (SDS), Kessler Psychological Distress Scale (K10), and EUROHIS-QOL 8-item index (EQoL) at intake and at approximately 30-day checkpoints. Analysis included descriptive statistics, paired t-tests with Bonferroni correction, standard error of measurement (SEM) for classifying improvement/deterioration, tertile analysis, and multiple linear regression.
**Key Results:** In the engagement dataset, 63% of new attendees returned at least once during six months, and over half of those returned weekly or more often. The most common activities were socialising with friends (89%) and using computers (48%). No significant demographic differences were found between those who returned and those who did not. In the therapeutic dataset, cannabis was the most common principal drug of concern (43%), followed by amphetamines (25%) and alcohol (21%). Fifty-two percent of clients completed only the first checkpoint assessment, but no significant differences in baseline scores or demographics were found between those with one assessment and those with multiple. Significant improvements (p < .001) were observed from intake to each timepoint for SDS, K10, and EQoL. At 90 days, 49% of clients improved on SDS, 70.7% improved on K10, and 51.6% improved on EQoL. The greatest effect sizes were for psychological distress (Cohen's d = 0.49 at 60 days). Tertile analysis showed that young people with the highest baseline substance dependence (mean SDS 8.63 to 4.72, a 45% decrease), highest psychological distress (mean K10 32.4 to 24.5, a 24% decrease, moving from 'severe' to 'moderate'), and lowest quality of life experienced the most positive changes, with improvements occurring rapidly within the first 30 days and maintained over 90 days. Regression analysis (n=1648) showed that improvements in SDS were independently associated with being female (b = -0.48, p < .01), higher baseline SDS tertile (Tertile 3: b = 2.56, p < .01), and changes in K10 (b = 0.12, p < .01) and EQoL (b = -0.06, p < .01), with the model explaining 37.2% of the variance.
**Clinical Implications:** The Street Universities model demonstrates that a low-threshold, strengths-based engagement program can retain a high proportion of disadvantaged young people, and integrating person-centred therapeutic interventions can produce rapid and substantial improvements in substance dependence, psychological distress, and quality of life, particularly for those with the highest needs. The findings support holistic, multi-domain interventions and suggest that improvements in one area (e.g., substance use) track with improvements in others (e.g., mental health, quality of life). The study highlights the importance of aligning engagement and therapeutic services to maximize impact for marginalized youth.