Place the lesson in your curriculum
This original Grade 2 lesson supports CCSS-M 2.MD.A.1 (choosing and using measurement tools) and 2.MD.A.4 (finding the difference between lengths). It is one classroom experience, not complete coverage or official certification. Check your district's sequence and required standards.
The standard describes the learning expectation. Your Teacher Teahouse curriculum map might place this lesson in a measurement unit after students have practiced using a ruler. The Mandarin language layer supplies the words, comparisons, gestures, and partner interaction needed to learn that content through Chinese.
放进课程地图，而不是把标准当教材
本原创二年级活动支持 CCSS-M 2.MD.A.1（选择并使用测量工具）与 2.MD.A.4（确定两物长度之差）。一节课不代表完整覆盖标准，也不是官方认证；请结合学区要求和已有课程进度。
标准界定学习要求；Teacher Teahouse 课程地图可以把此课安排在测量单元、学生练习使用尺子之后。中文语言层则提供词语、比较表达、动作示范和同伴互动，帮助学生通过中文学习数学。
Prepare two goals and simple materials
Content goal: measure two straight objects in centimeters and determine how much longer one is. Mandarin goal: report both measurements and explain a comparison using 比 and 长／短. These are lesson targets, not proficiency ratings.
Prepare centimeter rulers, pairs of paper strips cut to whole-centimeter lengths, a recording sheet, and a model ruler with a clearly visible zero. Use strips that fit the rulers. Avoid objects ending between marks in this first lesson; add those later when students are ready.
两个目标，几样简单材料
内容目标：用厘米测量两个直线物品，确定一件比另一件长多少。语言目标：报告两个长度，并用“比”和“长／短”解释比较。这些是本课目标，不是语言能力等级评定。
准备厘米尺、剪成整厘米长度的成对纸条、记录纸，以及零刻度清楚的示范尺。纸条不要超过尺长。本课先避免终点落在刻度之间的物品，待学生准备好再增加难度。
Make the vocabulary visible
Prepare eight cards: 长度 chángdù — length; 厘米 límǐ — centimeter; 尺子 chǐzi — ruler; 测量 cèliáng — measure; 长 cháng — long; 短 duǎn — short; 比 bǐ — compared with; 相差 xiāngchà — differ by. Pair concrete words with a ruler or strip drawing. Demonstrate 比 and 相差 with two aligned strips instead of inventing a misleading picture.
Keep numbers and units together: 12厘米, not only 12. Model moving a finger from zero to the endpoint. Ask students whether the ruler's physical edge always equals zero; use the actual markings to decide.
让词语和动作连起来
准备八张词卡：长度 chángdù、厘米 límǐ、尺子 chǐzi、测量 cèliáng、长 cháng、短 duǎn、比 bǐ、相差 xiāngchà。具体词配尺子或纸条图；“比”和“相差”通过两条对齐的纸条演示，不用含义模糊的装饰图片。
数字与单位一起出现：写“12厘米”，不只写“12”。手指从零刻度移到终点。请学生观察：尺子的边缘是否总是零？应根据实际刻度判断。
A 40-minute sequence
- 0–5: show two strips with their starting points misaligned. Ask which is longer and what needs to change to check fairly.
- 5–12: align a strip with zero, keep the ruler straight, and read the endpoint. Model one incorrect start and let students explain the problem.
- 12–22: partners take turns as measurer and checker. Each records both lengths and the unit; the checker remeasures before agreeing.
- 22–30: compare lengths and calculate the difference. For model strips of 12 cm and 8 cm, record 12 − 8 = 4 and say 红纸条比蓝纸条长4厘米。 Use your actual colors and measurements.
- 30–36: exchange strips with another pair. Explain the comparison without copying the first pair's answer.
- 36–40: each student measures a fresh pair and supplies a number sentence plus a brief spoken or written comparison.
40分钟课堂流程
- 0—5分钟：展示起点未对齐的两条纸条，问哪条更长，以及怎样才能公平比较。
- 5—12分钟：示范对齐零刻度、放直尺子、读终点；故意示范一次错误起点，让学生说明问题。
- 12—22分钟：同伴轮流当测量员和检查员，记录两条长度及单位；检查员重新测量后再确认。
- 22—30分钟：计算长度之差。示范纸条为12厘米和8厘米时，写12 − 8 = 4，说“红纸条比蓝纸条长4厘米”。颜色和数值以实际材料为准。
- 30—36分钟：与另一组交换纸条，重新测量并解释，不照抄答案。
- 36—40分钟：每人测量新的一对纸条，写算式，并用简短口头或书面比较作结。
A recording sheet and partner dialogue
Use these printable headings: 物品 A | A 的长度（厘米）| 物品 B | B 的长度（厘米）| 相差多少厘米？| 算式 | 我的解释. Leave generous space for a ruler sketch. If you distribute the sheet, add teacherteahouse.com at both the top and bottom.
Original model: 甲：红纸条长多少厘米？乙：12厘米。甲：你从哪里开始量？乙：从0开始。蓝纸条长8厘米。甲：哪一条更长？乙：红纸条比蓝纸条长4厘米，因为12减8等于4。 These are practice values, not answers to every pair's task.
可以抄用的记录栏与对话
记录栏：物品 A | A 的长度（厘米）| 物品 B | B 的长度（厘米）| 相差多少厘米？| 算式 | 我的解释。留出画尺子示意图的空间。发放打印练习时，在页面顶部和底部写上 teacherteahouse.com。
原创示例：甲：红纸条长多少厘米？乙：12厘米。甲：你从哪里开始量？乙：从0开始。蓝纸条长8厘米。甲：哪一条更长？乙：红纸条比蓝纸条长4厘米，因为12减8等于4。这些只是示范数值，不是每组任务的统一答案。
Different support, the same mathematical challenge
- More support: students point to the endpoint and complete ___长___厘米 with a word bank. Allow oral response or a labeled drawing when appropriate.
- Developing independence: students use ___比___长／短___厘米 and ask a partner to check the measurement.
- Extension: give two conflicting measurements. Students identify the likely error, remeasure, and explain their evidence. Do not require more difficult arithmetic simply because a student speaks fluently.
- Keep the intellectual work with the learner. A partner may help name a unit without measuring or answering for the student.
支持可以不同，数学思考不能被代替
- 更多支持：指向终点，用词库完成“___长___厘米”；按需要接受口头回答或标注图。
- 逐步独立：使用“___比___长／短___厘米”，并请同伴复核。
- 延伸：给出互相矛盾的测量结果，请学生找可能的错误、重新测量并说明证据；不要仅因中文流利就增加算术难度。
- 保留学生自己的思考。同伴可以帮助说出单位，但不要替对方测量或回答。
Use the work to plan tomorrow
Look separately for tool use, comparison reasoning, and Mandarin expression. If a student starts at the ruler's edge instead of zero, revisit measurement. If measurements are correct but the student adds the lengths, revisit what the difference represents. If the mathematics is secure but the explanation is brief, rehearse comparison language rather than repeating all the content.
For the next lesson, change the objects while keeping the unit consistent. Return to independent measurement before extending to estimates or different units. One correct response is a planning clue; repeated evidence across tasks gives you a better picture.
把学生作品变成下一课的依据
分别观察工具使用、比较推理和中文表达。从尺边而非零开始，要重教测量；测量正确却把两长度相加，要重看“相差”的意义；数学理解稳固但语言简短，则练习比较表达，不必重讲全部内容。
下一课可更换物品、保留相同单位。先再次观察独立测量，再延伸估测或不同单位。一次答对只是线索，跨任务的重复证据才能更清楚地呈现学习情况。