I commend children for giving volunteer service, yet I fully expect high school students to do better than library volunteer. Because this type of volunteer is not challenging enough for them. Thus, they are cheap substitute for real hard work.
Why do we have to ask others for volunteer opportunity instead of creating our own opportunities? High school students should rack their brains to be innovative and create their own work which is beneficial to both parties, if they do hope to excel. They deserve credit only if they can invent new ways to volunteer or use their grade level skills to serve. This reminds me of a young man who spent one summer organizing a rocket club among elementary school kids, an unusual experience, showing great leadership skills, and a success in the end. This young man was admitted by MIT.
The key is you don’t always do something that everybody does. You have to be unique. Even in volunteering, a leader is different from the crowd.