Background: Parenting programs have been shown to work when delivered to motivated ethnic majority parents in demonstration projects, but comparatively little is known about their impact when delivered to high-risk, multi-ethnic populations by routine local services. Methods: The Primary Age Learning Skills (PALS) trial was a randomized controlled trial of an evidence-based parenting-group program that targeted the parent-child relationship and child literacy. Parents of 174 children were selected from a population of 672 5- and 6-year-olds attending four primary schools in a high-risk, ethnically diverse, inner-city area. Eighty-eight children were allocated to the Incredible Years preventive program plus a shortened six-week version of the SPOKES literacy program, delivered by local services; 86 to usual community services; 152/174 (87%) of families were successfully followed up. Parent-child relationship quality and child behavior were measured using direct observation and parent interview; child reading was assessed psychometrically. Results: Two-thirds (58/89) of those offered the parenting program attended at least one session, with similar enrolment rates across the Black African, African-Caribbean, White-British and Other ethnic groups. Mean attendance was four relationship-building sessions and one literacy-development session. Satisfaction questionnaires were completed by 43/58 starters; 93% said they were well or extremely satisfied, with equally high rates across ethnic groups. At follow-up after one year, those allocated to the intervention showed significant improvements in the parent-child relationship on observation and at interview compared to controls; effects were similar across all ethnic groups. However, child behavior problems and reading did not improve. The cost was 1,343 pound ($2,100) per child. Conclusions: Programs can be organized to be engaging and effective in improving parenting among high-risk, multi-ethnic communities, which is of considerable value. To also be cost-effective in achieving child changes may require a set-up that enables parents to attend more sessions and/or an exclusive focus on children with clinically significant behavior problems.