Common exception words are words that do not fit usual spelling patterns. They are everyday words that children will frequently come across but that do not adhere to the usual grapheme/phoneme correspondences they have been taught about.
Here are the common exception words for Year 5 and Year 6:
accommodate, accompany, according, achieve, aggressive, amateur, ancient, apparent, appreciate, attached, available, average, awkward, bargain, bruise, category, cemetery, committee, communicate, community, competition, conscience, conscious, controversy, convenience, correspond, criticise (critic + ise), curiosity, definite, desperate, determined, develop, dictionary, disastrous, embarrass, environment, equip (–ped, –ment), especially, exaggerate, excellent, existence, explanation, familiar, foreign, forty, frequently, government, guarantee, harass, hindrance, identity, immediate(ly), individual, interfere, interrupt, language, leisure, lightning, marvellous, mischievous, muscle, necessary, neighbour, nuisance, occupy, occur, opportunity, parliament, persuade, physical, prejudice, privilege, profession, programme, pronunciation, queue, recognise, recommend, relevant, restaurant, rhyme, rhythm, sacrifice, secretary, shoulder, signature, sincere(ly), soldier, stomach, sufficient, suggest, symbol, system, temperature, thorough, twelfth, variety, vegetable, vehicle, yacht
Children are expected to be able to spell these by the end of Year 6.