加法和减法策略（7岁及以上）
Addition and subtraction strategies (age 7+)
运用位值和运算性质，解释加法和减法策略为什么有效。
Explain why addition and subtraction strategies work, using place value and the properties of operations
学习证据 / Evidence
- 解释为什么把十位和个位分别相加能得到正确的总数
- 描述为什么补偿策略有效（例如：“我多加了1，所以要减去1”）
- 用位值语言逐步说明书面计算方法的合理性
- Explain why adding tens and ones separately gives the correct total
- Describe why a compensation strategy works (e.g. 'I added 1 too many, so I subtract 1')
- Use place-value language to justify a written method step by step
评估问题 / Assessment
如果{{name}}用拆分法把“67 + 24”算成“60 + 20”和“7 + 4”，能不能用语言解释为什么这样算能得到正确答案？
If {{name}} works out '67 + 24' by splitting it into '60 + 20' and '7 + 4', can they explain to you in words *why* that approach gives the right answer?