The study aimed to investigate the retention of acquired argumentation and NOS conceptions among grade 10 students three months after the treatment. Thirty-six grade 10 students in two intact sections, randomly assigned into the Treatment and Comparison groups, participated in the study. The participants engaged in a treatment that lasted for four months and involved two units. Participants in both groups were involved in explicit argumentation instruction. However, participants in the Treatment group received the additional explicit NOS instruction. To assess the learning and retention of participants' argumentation skills and NOS conceptions, all participants responded to two open-ended questionnaires three times during the study (pre-, post-, and delayed post-test) followed by individual semi-structured interviews. Results showed that participants of the Comparison group, who engaged in explicit argumentation instruction only, mostly did not retain their argumentation skills, three months after the treatment. While participants of the treatment group, who engaged in explicit argumentation and explicit NOS instruction, mostly retained their argumentation skills and NOS conceptions after a three-month period following the treatment. These findings were discussed in terms of the following premises: prolonged contact with the content, distributed multiple experiences, meaningful cognitive connections, and NOS as a metacognitive tool.