This study examined the effects of a school/home-based intervention program designed to enhance the reading motivation and comprehension of Swiss fourth graders (N = 713). In order to identify the specific contribution of the home environment, the program was implemented in one group "without" (N = 244) and in one group "with" (N = 225) parental participation. The intervention was based on the principles of Self-Determination Theory (Deci & Ryan, 2002) and lasted one school year. Effects of the treatment were investigated in a pretest-posttest control group design with follow-up. Multilevel analyses showed that the school/home-based intervention had significant effects on reading enjoyment and reading curiosity. Effects on reading enjoyment were still detectable at 5-month follow-up. However, no effects were found for reading self-concept or reading comprehension. The findings highlight the potential of the family in the sustained promotion of reading motivation. (Contains 9 tables.)