1. I'm sorry that... [ex. I was so rude yesterday] 2. It's my fault. (= I am taking responsibility for the problem) 3. Oops, sorry. (for very small problems) 4. I should have... [ex. called you and told you I'd be late] 5. (formal) I apologize for... [ex. the delay]
Schools dont have a holiday if its not a weekly one. Students greet teacher and often send cards and presents. Teachers usually dont teach them from the books, those who do this share their experiences with the students. Students often try to surprise their teachers with anything they can think of.