More often than not students ignore the rules surrounding the correct grammar usage of "at." The word can be easily misused which is why many English teachers try to make it a point to illustrate the correct grammar usage of the word. Nonetheless, many students fail to retain the information. Perhaps it is in the way that the lesson is delivered or the way that the text book is written. Whatever the case may be, there are certain rules that surround the correct usage of "at."
Simply put, the word "at" is a preposition. A preposition is, in a sense, a connector. It connects words together. When you use the word "at" in a sentence you should notice that it smoothly connects the other words that are around it.
If the word "at" is not working as a connector then it will more than likely be working as an adverb. The word, when working as an adverb, will work towards modifying one of the words in the sentence. Some people call it a particle while others still maintain that the word is an adverb.
A preposition is a relationship word (hence the word connector). It is the sort of word that can explain the space, time or relationship of a sentence therefore linking the words together.
Believe it or not, there are only two rules that govern the use of prepositions like the word "at".
A preposition like "at" must follow certain words in order to make the relationship crystal clear between words in the sentence. In order to do this, for example, if you were to say the sentence "I am looking at him" you could only use the preposition "at." There is no way that you could use any other prepositions or the meaning of the sentence would be compromised and completely unclear.
The noun or pronoun counts as the object of the preposition. This can get a little tricky, but if you go back to the sample sentence, it can be a bit easier. The sentence used was "I am looking at him."
The analysis would go like so. The preposition is the word "at" which is followed by the pronoun him.
More often than not the innate understanding of the proper grammatical usage of a preposition such as the word "at" can be more than just a challenge. When students get into the whole notion of subjects, objects and trying to discern what the subject or the object of a sentence is, there can easily be a bit of a breakdown in learning.
As long as you remember that the preposition is the link, the connector or the relationship word that holds the sentence together and makes everything crystal clear, it will be slightly easier to digest the whole preposition lesson.
The idea that can make the lesson behind a word like "at" easier to understand, is how it fits into a sentence. "At" is the sort of word that can only fit into certain sentences, and when used, it can be slightly easier to understand how the word at "at" fits into the sentence as the perfect preposition.