Over the past 20 years, researchers have begun to examine data from asynchronous computer-mediated student discussions in courses. Some results have shown students to demonstrate lower or mid-level thinking skills, while others suggest students routinely demonstrate higher-order thinking skills. The authors investigated the relationship between scaffold types and the level of students' thinking skill performance, learning achievement and attitudes, in a two-by-two factorial, quasi-experimental study. Participants included 216 undergraduate preservice K-12 teachers who were presented with one of four versions of an asynchronous discussion board assignment. Resulting discussion interactions were evaluated for demonstration of low-, mid- and higher-order thinking skills. Findings revealed students who were given a scaffold demonstrated higher-level thinking skills more frequently than did students who received no scaffold. No significant differences in learning achievement associated with test performance were found in test results. The treatment variables did significantly affect effect survey ratings associated with students' attitudes.