tenses - "that one consider" or "that one considers"?

I have a question to ask regarding this quote.

In the formation of a marketing strategy, it is imperative that one considers the marketing mix, also known as the 4Ps – product, price, place, and promotion.

Should there be an 's' after consider?

Am I correct in saying that in a sentence like the one below, an 's' should follow the word consider?

It is imperative that the girl considers the marketing mix.

I seem to have seen similar sentences constructed both with and without the 's' after the verb before, e.g.

It is imperative that the girl go to school.

It is imperative that the girl goes to school.

Does this have anything to do with plurals and singulars, or with tenses?

Wow, this seems to be an awfully basic question but for some reason I just don't quite remember what should be done here.

(NOTE: The OP's question involves the mandative construction, one which might involve a subordinate subjunctive clause. -- F.E.)