(Image-Kris from Pixabay)
1) Catch up - reach the same level of progress as others, especially after falling behind. "After missing a week of classes, she had to work hard to catch up with her classmates."
2) Drop out - to leave school or college before completing a course of study. "He dropped out of university to pursue his passion for music."
3) Brush up on - refresh one's knowledge or skills in a particular subject. "I need to brush up on my Spanish before my trip to Mexico."