I think it should exist some kind of visual information saying what is new since (for example) the last commit or the last week. As this is a long list, when we access it we cannot know whether there's something new since the last time we visited the repository. You could have added some school which deadline is somewhere in May, and I might not see it.

Maybe another possibility is a separate section showing the current schools "accepting applications". I guess that who comes here has two objectives: or search what's available for applying, or see what past summer schools happened in the past. In this sense, two different parts in the README.md seem to me more friendly than just a long list.