The Summer after their Soph year they go to Mountain Warfare Training. (Scholarship Mids only).
The Summer after their Junior year they go to a 6 week version of OCS known as "Bulldog".
The Summer after their Senior year they go to The Basic School.
Then its off to MOS school and your unit.
Yes, they do CORTRAMID after freshman year if they are scholarship students. However, I've heard this year it's been cut back because of budget issues and some Marine Option Mids are not able to go to CORTRAMID.