Planning and conducting experiments require the application of the control of variables strategy (CVS). Research indicates that older children can learn the CVS by engaging in guided-inquiry activities. It has not been studied yet whether this is also the case for children as young as 6- to 7-years. 145 children aged 6-7 years participated in a study with a pre-, post-, follow-up test design comprising two experimental groups (EG 1, EG 2) and a control group (CG). EG 1 and EG 2 received a structured-inquiry lesson, thus, carrying out six predetermined experiments with an adult's implicit guidance. While the lesson in EG 1 was in the same physics domain as the test's physics domain, in EG 2 the lesson's physics domain differed from the test's domain. The CG did not experiment. We assessed children's CVS ability with a multiple-choice test. Results suggested that some children in the EGs learned the CVS, whereas in the CG, no learning effects occurred. However, most children in the EGs did not gain in the CVS ability, indicating that the small dose of six experiments in one physics domain was insufficient for learning the CVS.