In, on and at can be some of the trickiest English prepositions to learn correctly, but they are used very frequently, so you should take time to get familiar with when to use each one. This is UK English, so they say “at the weekend”. In North America, things happen “on the weekend”. We also use in/on/at to describe locations, so take time to find out what we use when!
Prepositions of Time in on at learning English grammar.
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