The boy is not a good student,who is dressed in school unifo

1 被从句“who is dressed in school uniform”修饰的,到底是the boy 还是a good student
答：修饰的是后者 a good student
如果修饰the boy 的话,句子的顺序应该如下：
The boy ,who is dressed in school uniform,is not a good student.
2 如果例句中没有逗号,情形又将如何?
答：同样是修饰后者 a good student
有逗号时从句是非限制性从句
无逗号时从句是限制性从句
但是修饰的成分是一样的