All levels:-ize or ise?

Many students ask me about the spelling of verbs ending in -ise or -ize, such as realise and organise and whether they should be spelt with  s or z. So I've been doing some research into the subject.

At first I thought that the -ize ending was American and the -ise ending was British, but it turns out that both are accepted in British English just as long as you are consistent within a piece of writing. Nevertheless, I would advise you to use the -ise ending and here is why:

While all verbs can be spelt with s, not all can be spelt with z. Some verbs such as advertise, advise, devise, are never spelt with z, not even in American English. You can check a list of these verbs here.