The most common and most likely answer to this crossword clue is the 6 letter word UPLIFT
I've seen this crossword clue in The Times
U
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More clues leading to the result UPLIFT
Buddy explains!

The straight part
We know that "Improvement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case improvement = uplift.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UPLIFT mean?
UPLIFT noun- The act or result of being uplifted.
- A tectonic upheaval, especially one that takes place in the process of mountain building.
- A brassiere that raises the breasts.
- To raise something or someone to a higher physical, social, moral, intellectual, spiritual or emotional level.
- (of a penalty) To aggravate; to increase.
- (travel) To be accepted for carriage on a flight.
- To remove (a child) from a damaging home environment by a social welfare organization.