What does "to pull your socks up" mean?

English Grammar Tests, Elementary Level

ESL/EFL Test #132 [color=blue]“Conversations and Comprehension (3)”, question 3

Mother: I just saw your report card and it looks like you will have to pull your socks up next semester.
Son: I know Mom. I will.
Mother: Good, because your grades are important.
Narrator: What does the mother mean?

(a) Her son will have to wear better clothing to school next semester.
(b) She believes that socializing with friends is a bad thing.
© Her son will have to work harder in school next semester.

English Grammar Tests, Elementary Level

ESL/EFL Test #132 [color=blue]“Conversations and Comprehension (3)”, answer 3

Mother: I just saw your report card and it looks like you will have to pull your socks up next semester.
Son: I know Mom. I will.
Mother: Good, because your grades are important.
Narrator: What does the mother mean? Her son will have to work harder in school next semester.

Correct answer: © Her son will have to work harder in school next semester.
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Whaat does “to pull your socks up” mean?

In the given context it means that her son will have to work harder in school next semester.[YSaerTTEW443543]

TOEFL listening lectures: Why does the professor mention Cygnus X-1?[YSaerTTEW443543]

This is a very clear and easy one.
Pull your socks up : want someone to work harder or to do better.
You can also say pull up your sucks.