The most common and most likely answer to this crossword clue is the 8 letter word REVISION
I've seen this crossword clue in The Guardian
R
E
V
I
S
I
O
N
More clues leading to the result REVISION
- Extremely reliable eyesight needed for a change
- Prerequisite for examination to do with eyesight?
- Preparation for an exam? That will make a change!
- Studying for an exam about conception
- Change concerning phantom
- Further study in theology faculty
- What students do with greater volume turned up, stifling volume
- Preparing for exam? That makes a change
- Change in respect of what might be conjured up for the future?
- Preparing for exam? That makes a change!
Buddy explains!

The straight part
We know that "Studying for an exam" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case studying for an exam = revision.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 REVISION mean?
REVISION noun- The process of revising:
- A changed edition, or new version; a modification.
- A story corrected or expanded by a writer commissioned by the original author.
- To provide with a new vision.