Derelict means abandoned. Dilapidated means badly looked after, whether or not anyone still uses it.
Both words describe something in a sorry state, so children reach for whichever comes first. But one tells you about the condition, and the other also tells you that everyone has gone.
Dilapidated is about repair. Grandad's shed might be dilapidated, with a sagging roof and a door that sticks, yet he still goes in every Saturday to fetch his tools. The building is in poor shape because nobody has fixed it.
Derelict adds emptiness. The old railway station at the edge of town, boarded up for years with weeds growing through the platform, is derelict: it has been left behind completely. A derelict building is almost always dilapidated too, but a dilapidated one is not always derelict.
Empty, abandoned and falling to pieces.
Similar: abandoned, ruined, dilapidated
Falling to pieces because it has not been looked after.
Similar: ruined, crumbling, shabby
In a cloze passage about a family living in a crumbling cottage, derelict is the wrong choice because someone still lives there. Spotting whether a place is abandoned or just neglected is exactly the kind of detail these questions test.
Definitions and example sentences on this page are the ones a child sees inside Wordrealm, taken from our list of over 1,100 words. It is free to browse, with nothing to sign up for.
Plain-English guides to each test, from the councils’ own pages: Kent Test · Medway Test · Bucks Secondary Transfer Test