Hello hhhhhhhhhhhg,

I commend students that complete the entire application process on their own because it means that they are motivated and independent. With that being said, proofreading is absolutely necessary. Whether its a native speaker or a college professor, you are most likely going to receive various feedback from them on the grammar, flow, and logical sequence of your writing. In most cases, high school admission counselors reviewing your application essays will look for an on-topic response that is from you and using your voice. So, refrain from hiring someone that will completely rewrite your essay for a fee.

很多学校的招生主管更喜欢看到学生自己写的个人文书。曾经帮助一位非常优秀的学生申请一所不错的学校，但因为招生主管认定个人文书非出自自己之手而拒绝。

你好：

最好找专业的顾问帮你，因为美高的学生并不清楚每个学校要求什么样学生。
每个高中都有自己的理念，如果不了解学校理念，不清楚学校需要什么样的学生，在短短的文书中无法展现出来，结果可想而知。

Native Speaker在文字，语法的润色上应该问题不大，但是你也要看是哪种程度的Native Speaker。