Can "In primary six " substitute for "When he was in primary six"?

His school results were always unsatisfactory for many years. When he was in primary five, he often talked to himself, raised his hands and pointed his fingers aimlessly, resulting in several complaints from his teacher. When he was in primary six, his teacher suggested a medical review by specialists at a hospital, so that he would be prescribed medication to control his condition in order that he would stop disturbing other children. However, I believed that it was his karma and he could only change through practising True Buddhism.

Can "In primary six " substitute for "When he was in primary six"?

Thanks.