One of the main difficulties with the English language is the often non correlation between the spelling of a word and its pronunciation. This simple exercise focuses students on phonetics, right from the start: a relatively simple way of checking the effective pronunciation of a word.
Of course this exercise is simply a first step, which can encourage the student and you the teacher to use this method from there on.
Explain that with online tools such as wordreference.com and others, you can check the pronunciation of a new word, not only hearing it but seeing it transcribed through phonetic symbols.
So much time and effort is wasted by not systematically checking in this way every new word learnt. Soon the student will gain more confidence and authority over the tricky world of English pronunciation.