This study examined effects of professional development for child-care staff on language acquisition of children ages 14-36 months. Child-care staff from 44 child-care centres agreed to participate in the study. Child-care staff from one-half of the child-care centres were randomly assigned to a one-time, four-hour workshop followed by three classroom visits over the subsequent three months. This treatment was designed to increase frequency and quality of joint attention episodes between the child-care staff and the toddlers. Child-care staff from the remaining 22 centres were assigned to a wait-list control group. Toddlers (N = 121) in both the groups (n[subscript treatment] = 64; n[subscript control] = 57) were assessed with a measure of language acquisition after six months. While there were no significant differences on total language acquisition between groups, treatment group toddlers whose child-care providers engaged in more frequent and longer bouts of joint attention acquired more language. The results of this study support that when child-care staff engage in longer and higher quality bouts of joint attention with toddlers they can affect language acquisition. (Contains 1 figure and 6 tables.)