Research Question: Among Southampton-area males arrested for and admitting to low-risk intimate partner violence as a first domestic offence and receiving a conditional caution, did a randomly assigned requirement to attend (with 5 to 7 other male offenders), two weekend day-long Cautioning and Relationship Abuse (CARA) workshops led by experienced professionals reduce the total severity of crime harm relative to a no-workshop control group? Data: Eligible offenders (N =293) were randomly assigned to the CARA workshop attendance requirement (n= 154) or to the no-workshop requirement (n = 139), with 91% of all cases receiving treatment as randomly assigned. Each offender’s records of police contact were tracked for exactly 365 days after the date of random assignment. Methods: All repeat arrests or complaints of crime naming the 293 randomly assigned offenders were coded by the Cambridge Crime Harm Index (CHI) as the primary outcome measure for each offender (Sherman et al 2016), with the sum of total days of recommended imprisonment for each offence (as the guideline starting point for sentencing) summed across all new offences, with both domestic and non-domestic relationships to their victims. Prevalence and frequency of repeat contact were also computed. All analysis was done by intention-to-treat. Findings: Offenders assigned to the workshop group were re-arrested for crimes with a total Crime Harm Index (CHI) value that was 27% lower than for re-arrests of offenders assigned to the control group (P =.011). The CARA workshop group members were arrested for crimes totalling an average of 8.4 days of recommended imprisonment under English sentencing guidelines, compared to an average of 11.6 days per offender assigned to the control group, the equivalent of 38% more harm without the workshop than with it. The effect size was much stronger, however, in the first study period of high caseflow (72% reduction in CHI, P = .001) than in the second period (21% reduction in CHI, P =.178). Frequency of re-arrest for domestic abuse (21% lower for workshop-assigned group) and prevalence (35% lower for workshop-assigned group) also favoured the CARA workshop group. Conclusions: The results of this one-year followup analysis suggest that the CARA workshops are an effective way to reduce the future harm of domestic abuse among first offenders who admit their crime, although effect size may vary over time. Given the highly restrictive eligibility criteria for the programme, these findings provide an evidence-based reason for testing the same treatment among a larger proportion of all first-offender arrests for domestic abuse. Keywords Intimate partner violence – policing – RCT—Crime Harm Index--CARA