Which of the following is NOT an essential element of a valid contract?

A valid contract is established based on several essential elements that must be present for it to be legally binding. Among these elements, legality ensures that the contract’s purpose is lawful; consideration pertains to something of value exchanged between the parties; and acceptance signifies that all parties agree to the contract terms.

Performance evaluation standards, while important in managing and assessing how effectively a contract is carried out, are not foundational elements that must exist for a contract to be valid. They can help in the administration of a contract but do not influence its initial legality or enforceability. Therefore, the absence of performance evaluation standards does not invalidate a contract, making it the correct answer to the question.