There are two programs from Google:
The summer of code targets university students and runs during the northern hemisphere summer. We were not part of it in 2014 and 2015 (they can't accept all organizations who apply, so they try to accept different ones each year).
The Google Code-In, started in 2010, runs during the southern hemisphere summer. It target 13-17 years old, so there are a few differences:
- Students don't get paid as contractors, instead this is more like a contest where the winners get to visit Google headquarters and the city of San Francisco.
- The tasks to complete are much smaller (usually 3 to 5 days of work maximum), and the students can complete many of them. In fact, only the 10 students who completed the most tasks can be selected as winners.
We have participated into the GCI since its initial run in 2010. Since the tasks are short, each organization can handle a lot more students, and in the first run there were only 8 organizations participating. This number is slowly growing, and this year they had 14 if I remember correctly. This means we get to handle hundred of students making their first contributions to open source projects.
In general, GCI is not really effective in terms of getting contributions to Haiku: the efforts the mentors need to put in is much higher than what would be needed for them to complete the tasks themselves. So it is more of a contribution to the open source ecosystem as a whole, lettign the students know about it and later become contributors to Haiku or other projects.
The Google Summer of Code targets more skilled students, with more ambitious project ideas. When it works well, the outcome is useful code for Haiku and the possibility to immediately get new contributors (myself being one of them, for example).