Dartmouth/Sandhurst/Cranwell teaches select individuals to be an Officer. Those Commissioned from the ranks have learnt how to be an Officer (my words).
Field Marshall Sir William Robertson has the distinction of being the only Private Soldier to have risen to the very top, becoming CIGS between the wars, he rose to Troop Sergeant Major before Commissioning and included a spell in jail for allowing a prisoner to escape. The only rank he didn't hold was WO1.