This study addressed one aspect of scientific reasoning, the control of variables reasoning scheme. We explored whether a short intervention aimed at accelerating this reasoning scheme by CASE lessons would improve students' ability to apply this scheme in problems related to the biology curriculum. About 120 students from grade nine were assessed for their Piagetian cognitive level and were divided into two groups, control or intervention. A short intervention of three sessions took place in the intervention group only. Both groups were then instructed on the topic of enzymes according to the biology curriculum and undertook a final exam. The results showed that only 20% of the population acquired the Piagetian formal operations level, in line with previous findings. In addition, it was found that the short intervention had a significant effect on students' ability to use the control of variables reasoning scheme.