There were several talks about "google code-in" (https://codein.withgoogle.com/), which is a program aimed at high-school students to get them involved in open source programs. Basically, programs setup "tasks" (which can range from "compile the project" or "write some documentation about X" to "solve a bug" or "refactor X", or probably even "improve test coverage", "make a tutorial video about an underrated feature", etc) and students earn "points" by completing them, over a six-weeks timeframe. Tasks are manually checked and validated by the project members (in <24h), so it requires dedication from several contributors to achieve this (apparently, there are quite a lot of students participating, so it also has the immediate side-effect of stress-testing the quality and efficiency of available project documentation and help channels).
I don't think we have the resources (in terms of people available, tasks, or doc) to participate in this year's edition (deadline is in 3 days), but I found the idea very interesting, and participating orgs reported that a lot of former participants stayed as long term contributors and even helped the next year's contestants.