The issue that makes it an unnatural English sentence is the article ("the school"). There may be very rare contexts where 'the school' would be right, but even then it sounds awkward. "School starts in September" is what should be accepted.

The schools starts in September is definitely INCORRECT. Could U please correct it?

To try to avoid the perfective issue, I wrote "School is STARTING in Spetember". Now it doesn't want the "ing"!!!