We examined the role child factors on the acquisition and transfer of learning the control of variables strategy (CVS) via instruction or self-discovery. Seventy-six fourth graders and 43 sixth graders were randomly assigned to a group receiving direct CVS instruction or a discovery learning group. Prior to the intervention, cognitive, scientific, and linguistic child factors were assessed. Acquisition and transfer of CVS knowledge were measured before and after intervention. Outcomes showed that CVS acquisition and transfer learning gains were higher for the instruction group than for the discovery group. Variation in CVS acquisition learning gains was explained by CVS pretest, verbal reasoning skills, and reading comprehension in the discovery group only. Variation in transfer gains were explained by vocabulary in the instruction group and by CVS prestest, verbal reasoning, vocabulary, and reading comprehension in the discovery group. It can be concluded that instruction provides a more effective method for learning CVS since individual differences in the instruction group played a marginal role explaining CVS posttest. However, since individual differences in linguistic ability account for variation in CVS learning gains discovery learning, these should be taken into consideration when teaching CVS in a more discovery-based manner.