Is it a good idea to include participation in summer schools in my CV? Is it a good idea to include participation in summer schools to my CV?
I assume you're talking about summer schools aimed at teaching graduate students or postdocs about recent developments.  At an early career stage, it's certainly worth listing participation on your CV.  If you're a beginning graduate student, then you probably don't have a lot of other things to list, and attending a summer school means something (namely that you are energetic and eager to learn, and that your application was strong enough to be accepted).  It's not a big deal, but listing it in your CV can't hurt and might help a little.  

As you progress in your career, it becomes less and less relevant.  Eventually you'll probably delete it, on the grounds that when you're coming up for tenure, nobody cares at all whether you once attended a summer school for grad students.  But it doesn't really matter exactly when you delete it.  You can safely wait until you start to wonder why you are bothering to include it when you have so much more impressive things elsewhere on the CV.