Past work has shown that generating explanations can improve both comprehension and metacomprehension outcomes. Although practice testing may sometimes improve comprehension, it is unclear if it affects metacomprehension (the ability to monitor one's understanding). The current study tested whether online homework activities involving practice testing alone might improve comprehension and metacomprehension when learning from textbook excerpts in an introductory science course, or whether engaging in explanation activities is critical for better outcomes. Results showed that practice testing did facilitate comprehension of the studied topics, but it failed to improve skills in comprehension monitoring on a new set of topics and exacerbated overconfidence. In contrast, metacomprehension accuracy increased when students generated explanations as part of online homework activities.