In Germany we have political parties that are open and that matter in the political landscape. If you want to do something about a political issue then it's very ineffective to see yourself as an activist because that means you usually aren't around the people who make policy decisions and you are an outsider from their perspective.
In Berlin there's nothing stopping a high school student from sitting in the rooms in which the educational policy agenda of the main political parties is made.
The adult might even like having you there to have your perspective which is different from their own. That doesn't mean that they will do everything that you want, but you might contribute ideas.
In Germany the recommendation would be to focus on joining one political party and paying your dues in it. Pick one political issue in which you want to contribute. Research that issue and try to get motion on the topic passed within the party infrastructure. At best you also read what other people outside of your party have to say about the issue.
If you are in the process of writing a motion on topic X, it might be easy to simple tell other civil society actors in that space to say: "Hey, I'm in the process of writing a motion on topic X for the next party congress of party X. I want to have your thoughts on the matter." Then you go out and meet people to refine your thinking. The best learning happens by talking to knowledgable people
Solving societal issues is not about doing the obvious things but about understand the issues and the stakeholders in the issue.
Focus your energy. I don't see a reason why you shouldn't be able to contribute. Most people don't produce change because they don't focus or because they rather associate with people who are like themselves than sitting in rooms with serious people.
Doing this builds also the connections that you need to have a political career in Germany.
Suppose a high school student is deeply interested in a particular social or political issue and interested in doing something about the subject. What advice would you give him/her?
You may assume that the high school student is roughly similar in profile to the typical active LessWrong participant when he/she was in high school.
Some candidate social and political issues are listed below.
Topics of particular interest to the LessWrong audience:
Others that are more commonly perceived as important issues in the world today:
I asked a few people to opine on the last two issues on the list (in Facebook posts linked above) and the respondents generally focused on the acquisition of background knowledge rather than direct activism (i.e., read and learn rather than proselytize). Prima facie, this seems like sound advice. But it's quite possible that the set of people I interact with on Facebook is biased in favor of armchair stuff to the exclusion of activism. What do people here think?
Feel free to pick on one particular item in one of the above lists, or something not on either of the lists, and provide a specific answer for that. Or, provide general guidelines. Also feel free to specify additional assumptions (such as the country the student is in, or the student's other abilities or interests) and answer within the constraints of those assumptions.
PS: For some of the issues, you may feel that the issue is overrated or misguided (for instance, you may think that global warming is a non-issue, or that the status quo is optimal with respect to civil liberties or migration policy). In this case, your advice to the hypothetical high school student might largely be directed at making him/her come around to your point of view of the irrelevance of the issue. Comments suggesting you'd give advice of that sort are also welcome. If you'd simply suggest to the high school student to refrain from thinking about socially or politically charged topics entirely, that would also be interesting to know (cf. politics is the mindkiller).