A teen wants a new life but his bad past keeps holding him back.

Write down where the teen is in life (bad past or bad present). Now write as far as believably possible away from that. This is the journey. Describe that and what is preventing it.

A teen from a ghetto wants to be the first person he knows to attend college but a racist principal and a broken education system stand in his way.

Not perfect, but more specific.

Here is a page that explains the function and basic construct of a logline:
https://loglines.org/howto/

Hope this helps.

Here is a page that explains the function and basic construct of a logline:
https://loglineit.com/howto/

Hope this helps.