The general definition of an exclamation is an utterance that expresses an emotion such as surprise, anger or admiration. In the National Curriculum the term is used is a specialised way. Exclamations in the NC are defined as having a particular structure: they need to contain what or how. For example, What a wonderful sight they are! What a beautiful day! How amazing you are! Please note that in the NC an exclamation mark after a sentence is not enough to turn it into an exclamation (defined as a pattern with what or how), so the following sentence is not an exclamation, but a statement, despite the exclamation mark: This is a wonderful event! We see in this last example that it's perfectly fine to add an exclamation mark after sentences that do not have what or how in them; it's just that in the NC they are not exclamations, because these are defined as particular structural patterns.