Only recently has cognitive load theory been applied in conceptual change approaches. To our knowledge, ours is the first study to examine the effects on students’ cognitive load of an approach contrary to a refutation text design. We combined computer and textbook instruction with involving alternative conceptions (ACs) to instruct 398 9th graders. We determined the number of scientific conceptions learned within a pretest, posttest and retention test design while measuring the students’ mental effort during the instruction. The groups whose instruction involved ACs did not show any significant long-term increase in the number of scientific conceptions learned compared to the control group. The textbook instruction with ACs resulted in the students unnecessarily investing higher mental effort. Further research is needed to clarify the effect.