May. These are referrals. Some teachers choose to send other grades at this time, but is not required. These are not final grades. They do not go onto the transcript. They are provided to warn both students and parents that a problem exists in a particular class.
High school grading and reporting works the same way in a school on the quarter system.
Except for grades in Math 1H, French 1CP and Spanish 1CP, middle school grades are on a transcript separate from the high school transcript.