When to use a or an:
If the word starts with a consonant sound, then ‘a’ should be used (for example, ‘a rock’). If the word starts with a vowel sound, then ‘an’ should be used (for example, ‘an ice-cream’).
Many children will already know this by Year 3 and use these instinctively when they talk. The challenge is to remember to use the right combination in their writing.
Words beginning with an unstressed ‘h’ can also be tricky to remember (for example, ‘an hour’ or ‘an honest man’)