I'll have to disagree with Henning. Most "summer schools" in computer sciences are not schools. They are not credit bearing, are short in duration, and consist of talks and workshops by active researchers in computer science on topics of research interest; attenders are also usually not required to be students (they could be professionals or even faculty themselves). Moreover, attending them don't enroll you in a program of academic study.
If they meet those criteria, they are a form of academic conference, not a program of study. You should therefore state that your purpose of visit is business/cultural, not study. If the summer school is credit-bearing or does constitute a program of academic study, though, then you will indeed be studying.