What qualities are organizing committees looking for in a reference letter for a summer school?

How would you write a reference letter for someone who is applying to a summer school intended for Ph.D. students/postdocs? The summer school only lasts for 3 days up to a week and I am curious as to what qualities and traits the organizing committee is looking for in participants. Do the participants have to be able to think very fast, for example?

What skills are sufficient to be able to participate in a summer school successfully? I am writing a reference letter for someone who is relatively new to a field and is interested in doing research on topics relevant to the summer school. The student has more or less the prerequisite knowledge needed for this summer school if that's worth mentioning. Also, the student is seeking for funding so I want to be serious about this letter.

From where I'm from, there weren't many opportunities for summer schools so I would appreciate your suggestions.

Thanks!