我们学校的理工科成绩都被压得特低。学校一般怎么查呢，如果我们学校没上网公布成绩的话？

Just explain the grading policy of your school in your optional essays. It is really dangerous to forge one's transcripts in any way. Some business schools may send a request form directly to your school to check the real transcripts out, or even hire an agent to do so in person. So, just explain it and make your essays stronger. My two cents. Good luck.

But the school doesn't care the difference of grading systems at all. Your lower GPA will make the school's average GPA lower, which will make the school's overall ranking lag.