Causal reasoning is an important part of scientific thinking, and even young children can use causes to explain what they observe and to make predictions. Weight is an interesting type of cause because it is a nonobvious property, and thus is not readily observable. The first research question of my dissertation examines when children use this property as a cause. In Study 1, 2- to 5-year-old children completed three different tasks in which they had to use weight to produce effects; an object displacement task, a balance-scale task, and a tower building task. The children’s use of weight improved with age, with 4- and 5-year-olds showing above-chance performance on all tasks. The younger children’s performance was more variable across tasks, suggesting that the complexity of the problem may influence their use of weight. The second research question is whether children’s use of weight as a cause can be improved. To examine this question, I varied the pedagogical cues that children received on the balance scale task from Study 1. The results of Study 2, indicate that highlighting the different effects of the heavy and light objects improves 3- to 4-year-olds’ performance. However, the results of Study 3 indicate that 2-year-olds did not benefit from even multiple pedagogical cues (contrasting the different effects and providing a verbal description to highlight the weight difference). To sum up, children at age 4 and above showed a general ability to use weight in across causal reasoning tasks. Whether children’s understanding of weight could be improved depended on their age and the cues given.