我国《义务教育法》规定：凡年满6周岁的儿童，父母及其他监护人应送其进入学校接受义务教育。按照我国学校实行每年9月1日一次入学的规定，凡当年8月31日前年满6周岁的儿童可进入学校接受义务教育，而当年9月1日及以后满6周岁的儿童则必须晚一年入学。严格的入学截止日期限制使得原本随机的出生日期变得有差异，如果严格按照规定入学，8月份出生的学生将成为同年级中相对年龄最小的， 9月份出生的学生成为相对年龄最大的，而且无论截止日期如何调整，同年级同学中的相对年龄依然存在。每年开学季，严格的入学年龄限制都成为公众普遍关心的教育话题，尤其是孩子出生在入学截止日期前后的父母，更加关心相对年龄对孩子未来的学习、生活带来的影响。那么相对年龄是否会对学生的学校表现产生影响呢？如何解释学生相对年龄对学校表现的影响呢？ 本研究使用中国教育追踪调查2013-2014基线数据，通过多元回归分析的方法，探究相对年龄对七、九年级学生学校表现的影响。结果表明对于全样本，相对年龄对学生的学校表现有显著的负向影响，相对年龄越大的学生，其认知表现和由学校适应所代理的非认知表现都较差。相对年龄每减小1岁，七年级学生的认知能力得分提高约0.25个标准差，非认知能力得分提高约0.12个标准差；九年级学生认知能力得分提高约0.21个标准差，非认知能力得分提高约0.04个标准差。家庭社会经济地位越高，相对年龄对学生认知能力的影响系数越大，家庭社会经济地位起正向调节作用。通过分析相对年龄效应存在的原因，得出如下发现：（1）相对年龄较小的学生所感知到的教师期望更高，进而认知表现更好，教师期望在相对年龄和认知表现之间起部分中介作用。（2）相对年龄越大的学生，越难在同班同学中建立稳定的同伴关系，进而非认知表现较差，同伴关系在相对年龄和学生非认知表现之间起部分中介作用。对于严格按照规定入学，且无留级或跳级经历的学生而言，相对年龄对其认知能力有显著的负向影响，对其非认知能力无显著影响，相对年龄每减小1岁，七年级学生认知能力得分提高约0.15个标准差，九年级学生的认知能力得分提高约0.17个标准差。

The “law on compulsory education” in our country stipulates that parents and other guardians should send children who are over the age of 6 years old to school to accept the compulsory education. According to that the start day of our school is September 1 every year, all children over the age of 6 before and in August 31 can enter school to accept compulsory education, and all children who reach the age of 6 after and in September 1 must be one year late to school. Strict admission cut-off makes original random birth date different. In this way, if everyone enters primary school in strict accordance with the provisions of the entrance, students who are born in August will be the youngest pupil in the same grade, while students born in September to be the oldest students. And no matter of how the cut-off is adjusted, the relative age in the same grade still exists. Annual back-to-school season, strict entrance age rule has become public widely concerned educational subject. Especially parents with children who are born around the cut-off date care more about the relative age effect on children’s future study and life. So does the relative age have an influence on students’ school performance? How to explain the influence of students' relative age on school performance? This study uses China Education Panel Survey data from 2013-2014, through multiple regression analysis, to explore the influence of relative age on school performance of seventh and ninth grade students. The results showed that for the full sample, the relative age has a significant negative influence on students’ school performance and students with older relative age have poorer cognitive performance and non-cognitive performance which is agented by school adaptation. One year decreasing in relative age makes the cognitive ability score of seventh grade students improve by about 0.25 standard deviation, and the non-cognitive ability score improve by about 0.12 standard deviation, and for ninth grades students, it’s about 0.21 standard deviation and about 0.04 standard deviation. The higher the family social economic status, the greater influence of the relative age on students' cognitive ability, and the family social economic status has a positive regulating effect. By analyzing the reasons for the existence of relative age effect, this research find that: (1) Students with younger relative age have higher teacher expectation and then have better cognitive performance. Teacher expectation play partial intermediary effect between relative age and cognitive performance. (2)The older in relative age of the student, the more difficult it is to establish a stable peer relationship among his classmates, and then the non-cognitive performance is poorer. Peer relationship plays partial intermediary effect between students’ relative age and non-cognitive ability. For students who are in strict accordance with the provisions of the entrance, and no grade or advanced placement experience, the relative age has significant negative effect on their cognitive ability, and has no obvious effect on non-cognitive ability. One year decreasing in relative age makes the cognitive ability score of seventh grade students improve by about 0.15 standard deviation, and for ninth grades students, it’s about 0.17 standard deviation