Explain to the interviewer any necessary context so that she can understand the circumstances you faced.
Keep this part of your response brief, as you should focus the conversation on the process of overcoming the challenge rather than the initial struggle.
As you prepare for the interview, keep the purpose of this type of question in mind.
The interviewer isn't necessarily interested in hearing about some horror story from your past.
Alternatively, you could talk about a specific competition that was especially challenging.
Just frame your answer to reveal your problem-solving abilities.
Your first step is to figure out which challenge you want to share with your interviewer.
It's wise to shy away from anything that's too personal—you don't want your interviewer to feel uncomfortable.
But an appropriate challenge can come in many forms.
If you struggled, but ultimately succeeded, in a specific class, you might find this to be a perfect topic to discuss during your college admissions interview.