- One of my students needs more speaking PRACTICE
- One of my students needs to PRACTISE their speaking more
In the first sentence, PRACTICE (with an ICE) is a noun; in the second, PRACTISE (with an ISE) is a verb.
There are similar pairs of words, such as LICENCE / LICENSE (same pronunciation) and ADVICE / ADVISE (careful, the pronunciation is different!)
Listen to the difference:
If you know of others which follow this rule, send them in.