Explanation:

- The sentence is comparing a kid to others in the school. It implies the kid has a unique level of intelligence.

- smartness: (Option 1) is a noun that refers to the quality of being smart. It's not suitable as it doesn't fit the grammatical structure of the sentence.

- smarting: (Option 2) is a present participle of the verb "smart," which means to cause pain or discomfort. It's irrelevant here.

- smarter: (Option 3) is a comparative adjective that compares two entities. Since the sentence involves one entity being the best among all, this option is not suitable.

- smartest: (Option 4) is a superlative adjective used to indicate the highest degree of an attribute. It fits perfectly in the context of being the singular best among many.

Correct Answer: smartest (Option 4)