1 to go to school

2 to attend school

1 middle school

2 classifier: 个 gè

1 chemistry

2 chemical

1 to study at the same school

2 fellow student

3 classmate

4 classifier: 位 wèi

5 classifier: 个 gè

1 (in) return

2 reciprocation

3 payback

4 retaliation

5 to report back

6 to reciprocate

1 to take sth as a lesson for next time (idiom)

2 once bitten, twice shy

1 without learning or skills (idiom); ignorant and incompetent

1 not ashamed to learn from subordinates (idiom)

1 to return good for evil (idiom)

2 to requite evil with good

1 to repay kindness with kindness, and repay enmity with justice (idiom, from Analects)