The present article reports results of a real‐world effectiveness trial conducted in Denmark with six thousand four hundred eighty‐three 3‐ to 6‐year‐olds designed to improve children's language and preliteracy skills. Children in 144 child cares were assigned to a control condition or one of three planned variations of a 20‐week storybook‐based intervention: a base intervention and two enhanced versions featuring extended professional development for educators or a home‐based program for parents. Pre‐ to posttest comparisons revealed a significant impact of all three interventions for preliteracy skills (= .21–.27) but not language skills (d = .04–.16), with little differentiation among the three variations. Fidelity, indexed by number of lessons delivered, was a significant predictor of most outcomes. Implications for real‐world research and practice are considered.