Piero - llegando, llegaste

hello Pau_GyG
I was born and raised in Mexico, so am fairly familiar with spanish and local idioms, but would like your help in translating a song or two by Piero.
let's start with the song "llegando, llegaste", I understand that piba translates to girl or chick but need help with the following two phrases
"no pensaba en las materias" and "y siempre me hacia la rata con el pibe de a la vuelta."
thank you for any assistance you may provide.

Just going by the context provided, I'd say the first phrase means "I (or He/She) wasn't thinking about schoolwork" and the second one means "and I was always behaving like a rat with the 'chick' from around the corner." I hope this helps.

"Hacerse la rata" is "to play truant (or 'hooky')". I was always playing truant with the BOY from around the corner.

thank you both bedroomeyes and momper, much appreciated.