In English, both "at the beginning of September" and "in the beginning of September" are sometimes used interchangeably to mean the same thing — the early part of September. However, "at the beginning of" is considered more standard and more commonly used. It indicates a more precise point in time, typically the first few days of the month, week, etc. For example: 1. "School will start at the beginning of September." — This would generally be understood to mean school starts during the first few days of September. The phrase "in the beginning of" is often less preferred in this context, and some style guides may even consider it incorrect. However, it's still understood by most English speakers. If used, it typically carries the same meaning as "at the beginning of," indicating the early part of the time period. For example: 2. "School will start in the beginning of September." — This sentence, while less standard, is still understood to mean school starts during the first part of September. When in doubt, use "at the beginning of" for clarity and conformity to standard English.

The difference between "at the beginning of September" and "in the beginning of September" lies in the prepositions used, which can subtly alter the meaning of the sentence. "School will start at the beginning of September." This sentence indicates that the start of school will specifically occur at the precise time when September begins. It suggests a more exact or specific timing, pinpointing the very beginning of the month. "School will start in the beginning of September." In this sentence, "in" is used instead of "at." It implies that the start of school will take place sometime within the general time frame of the beginning of September. It does not specify an exact date but rather suggests a period within which the school will commence. Both phrases convey a similar idea of school starting in early September, but "at the beginning" is more precise and implies a specific point in time, while "in the beginning" is more general and suggests a broader time range.