The study involving 209 high school students in an instructional program about comma rules was an attempt to test the concepts of cognitive load theory in a real classroom setting. It investigated the effects of (a) cued versus conventional problems and (b) blocked versus random problem presentation sequence during practice on the performance and perceived mental effort of lower- and higher-achieving students. The researchers anticipated that cued problems would reduce learner extraneous cognitive load while random problem presentation sequence would increase germane cognitive load. The researchers also predicted that expected effects may not hold true for higher-achieving students. The treatments yielded a near-significant interaction effect for mental effort ratings indicating that conventional problems may have appeared harder to lower-achieving students while cued problems may have appeared harder to higher-achieving students. There were no notable performance differences. Issues related to researching cognitive load theory effects in a real classroom setting are discussed. Copyright © 2006 John Wiley & Sons, Ltd.