The construction industry consistently ranks as one of the most hazardous in the U.S. for both fatal and non-fatal traumatic injury rates.1,2 Construction work accounts for the highest number of fatal occupational injuries in the U.S., and this number is increasing. Falls from heights remain the leading cause of fatal traumatic injury in this industry, followed by struck-by incidents, and contact with an electric current. Significant challenges to reducing injury rates include worksite and job task characteristics, work organization, worker training, and an increase in the informal work sector, which has been accompanied by an increase in the proportion of immigrant workers. In 2000, the proportion of self-identified Hispanic workers in construction reached 15%, of whom 74% were born outside the U.S. and nearly one-third spoke only Spanish. The rate of fatal occupational injury in this population was almost twice that of other construction workers (relative risk [RR] = 1.84, 95% confidence interval [CI] 1.60, 2.10).2 The effect of immigration status overlaps with reports of ethnicity. Of the 2.3 million foreign-born construction workers in the U.S. in 2005, 59% were born in Mexico and an additional 25% were born in other countries in Latin America. By 2005, 27% of construction workers self-identified as Hispanic and one-quarter of construction workers reported speaking a language other than English in the home.3 Loh and Richardson explored all traumatic occupational fatalities reported through the Census of Fatal Occupational Injury between 1996 and 2001, and determined that the excess rate of fatal injury among Hispanic workers occurred only among foreign-born Hispanic workers, while U.S.-born Hispanic workers had fatal injury rates that were identical to the rest of the U.S. workforce.4 Occupational safety and health training programs and effectiveness research have explored primarily the effectiveness of safety and health training in fixed-site manufacturing and among hazardous waste workers. This research was spurred chiefly by the Occupational Safety and Health Administration (OSHA) Hazard Communication Standard and by the Superfund Amendment and Reauthorization Act of 1986, both of which expanded requirements for worker training. Active participation in problem identification and problem solving contribute to effecting measurable change.5–8 However, peer-reviewed evaluation of the effectiveness of training in the construction sector is limited. A study of plumbers and pipefitters in western Ohio demonstrated a reduction in injuries among workers who had received jobsite safety orientation, although the impact of safety awareness training (equivalent to the OSHA 10-hour course) could not be determined.9 Dong et al. evaluated health insurance records, union training records, and workers' compensation data for the two-year period 1993–1994 for more than 8,000 laborers in Washington State. Laborers who had completed an OSHA training program experienced a 12% decrease in workers' compensation costs (95% CI 0.75, 1.02).10 Studies of workplace health and safety also emphasize the importance of factors such as supervisory support, provision of appropriate equipment, training on use of equipment, and active worker participation, among other considerations that determine safety climate—the perception by workers that safety is valued in their organization.11–13 The importance of reinforcing classroom learning with on-site job safety has been emphasized for younger workers in particular. In one study of youth in farm settings, safety training of the youth alone failed to have any impact.14 A recent study of apprentice (novice) carpenters beginning on-the-job training in residential construction demonstrated wide variability in the quality of jobsite mentoring that often resulted in a lack of support for safe work practices learned in the classroom and consequent failure to follow them.15 A growing body of information evaluating the role that safety climate plays in general industry has more recently been applied to construction sites.16–22 Safety climate has been associated with injury occurrence and with injury severity in construction workers,19,20 and appears to be linked to injury and illness in Latino poultry workers.21 To address the unique challenges posed by construction sites, OSHA adapted its 10-hour hazard-awareness training program to specifically target construction workers. CPWR (formerly the Center to Protect Workers' Rights, now the Center for Construction Research and Training) subsequently developed the Smart Mark curriculum for the OSHA 10- and 30-hour training programs for the members of building trades unions under the guidance of the Construction Industry Partnership in 1997–1998. Smart Mark hazard-awareness training is frequently incorporated into the apprenticeship (or pre-apprenticeship) training programs for the building trades, and is presented differently to apprentices (i.e., students enrolled in formal training that includes practical experience as well as classroom teaching) and journeymen (i.e., workers who have entered a trade and are working for others). The 10-hour program includes up to 10 of the 13 available training programs or modules, selected on the basis of relevance to the particular trade. Apprenticeship programs vary in length and content by trade, but in general alternate classroom, hands-on controlled workshop activities, and actual on-the-job experience in work settings. This pilot study was conducted to (1) assess the impact of hazard awareness training on baseline knowledge, attitudes, and work practices among roofers and pipefitters and (2) identify potential changes in safety climate. Because one of the unions included a significant proportion of members who were born in Mexico, demographic differences were explored in this group. This article describes baseline demographics of participating workers; the relationship to baseline knowledge, attitudes, and self-reported practices regarding fall and electrical safety hazards; and changes in knowledge and attitudes following the training intervention among a paired subset of workers.