There’s further illustration in the entries on alphabet
(which is a more general notion). Examples of accents in English can be easily tracked down from a dictionary of foreign words in English, such as John Ayto, Making Sense of Foreign Words in English
(Chambers, 1991), but I imagine most of these words and phrases are too difficult for younger students. It can be interesting to go out looking for accents (in posters, shop signs, product labels, ads, newspapers, comics). Other aspects: pick out cases where the accent is really needed to distinguish words (résumé vs resume, learnèd vs learned
); work out which sounds are signalled by an accent, in a language; look at the range of accents in familiar foreign languages (anyone brought a foreign paper or magazine back from abroad?); look out for idiosyncratic uses of accents, such as the metrical marks sometimes shown on line of poetry.
Incidentally, the mnemonic on grave and acute only works because we read English from left to right. In a language where the direction was the other way (eg Arabic), the impression would be the reverse.