Contrary to popular belief, spelling words such as maximise with a z isn’t a recent American innovation. The English language has always recognised variant spellings using both –ise and –ize suffixes.
ise or ize
Noah Webster (1758–1843), a teacher in Hartford, Connecticut, believed that the English language suffered from an excess of pedantry which he blamed on the British aristocracy. Even today, debates over English spelling invariably involve discussions about the Greek and Latin roots of the language.
Webster argued that the language should be guided by “the same republican principles as American civil and ecclesiastical constitutions”—in other words, by popular usage. So he set about producing his own dictionary, which went on to become a cornerstone of teaching English in America and was in part responsible for the now-familiar spelling bee. Over the course of more than 300 editions, he made many changes including adopting the ize ending, dropping the u from words like colour, and switching around the e and r in words like centre.
It may come as a surprise to learn that the bastion of the English language, The Oxford English Dictionary, has always favoured –ize, on the basis that the suffix derives from the Greek suffix –izo. In contrast, most other dictionaries reflect the adoption of the –ise ending for words that entered the language via French, which uses -ise.
When to ise or ize
But there are some words that should never be spelt with a Z. These include words which do not derive from the -izo suffix, but from a different root which coincidentally ends in –ise. Examples include vise (revise, advise), cise (exercise, incise) and prise (enterprise, compromise, surprise). Misguided simplification of the rule to universally replace Zs with Ss has also led to mistakes such as analyze which is, well, wrong—although Microsoft Word doesn’t have a problem with it.
Which alternative you choose is unlikely to greatly affect the impact of your message. If your proposition is compelling and well crafted, even the most steadfast pedagogue will focus on what you are saying, not whether you’ve used Ss or Zs—so long as you are consistent.