Things improved even more in the evening, when dad let me go to the cinema with my friends, as a reward for getting such good results at Maths.

reward 是名词，意思是"奖励、回报"，指对某人良好表现或成就给予的正面反馈或奖赏。这个词来自古法语，由 re-（表示"回"）和 ward（"看护、关注"）组成，原意是"回报关注"，引申为"奖赏"。