Can I get a visa to study in the United States one month before the start of school? What if I need to leave early in July?

Yes, this is the rule, but you can do it in advance:

If you want to enter the country in advance, you can only apply for a B2 visa again, and then apply for a transfer after entering the country.

Some of them came early, but most of them were refused entry and returned by the original plane.

According to the regulations of the Department of Homeland Security, all students studying in the United States for the first time can only enter the United States 30 days or less before the start date indicated on the I-20 form. Please fully consider this time rule when making travel plans to the United States. Students who need to enter the United States longer in advance (more than 30 days before the start date) must obtain a short-term visit visa to the United States. There will be a note on his/her short-term visit visa indicating his/her expected student status. In addition, the applicant should fully explain the purpose of his/her visit to the United States to the immigration inspector in the United States at the port of entry. Before he/she starts studying, he/she must also obtain approval to change his/her status, including filling out an application form for changing his/her non-immigrant status (I-506 form) and submitting an I-20 form to the office of the Department of Homeland Security that proposes to change his/her status. Please note that the application fee is $ 140, and the applicant cannot start studying in the United States before the application is approved.