A: What do you plan to do in holidays?
B: I 'll have to study.
B: I got a very bad school report this term. If I don't pull up my socks. I'll be lagged behind by the class.
pull up one’s socks
exp. To make a redoubled effort; to make a sincere attempt to improve. （加倍努力，真心地尝试去提高）
e.g. After that abysmal grade on my midterm exam, I'm going to have to really pull up my socks if I want to pass math this year.
e.g. John, if you don't start pulling up your socks, we're going to have to give your job to someone else.
e.g. If he's hoping to gain promotion he will have to pull his socks up.
e.g. His teachers told him to pull his socks up, or he'd undoubtedly fail his exam.
1. lag behind：落后
e.g. If we walk slower than the others we shall lag behind them.
e.g. She is very strict with herself in her English study and unwilling to lag behind.
2. school report：学生成绩报告单
e.g. Could you bring your birth certificate and your last school report with you?
e.g. I got an unfavourable school report this term. ( an unfavourable school report：一份分数不佳的报告单)