Como dizer “Fazer escola” em inglês

Zumstein
I can't think of an expression similar to "fazendo escola", but there are ways to express the concept.

The abandoning of the municipal assembly sessions by the opposition parties is gathering (or encouraging) followers in the region.

Another expression could be "increasing the fold or flock", which is quite often used by the church, but can be used in this context too.

The abandoning of the municipal assembly sessions by the opposition parties is increasing the fold (or flock) in the region.

Outra opção:

Become common

''Students are now used to appealing for work to be remarked at school, and increasingly this practice is becoming common at university level too.'' [Google UK]

''The abandoning of the municipal assembly sessions by the opposition parties is becoming common in the region.''

My suggestion:

To set a precedent.

By appealing to work to be remarked at school, students have set a precedent and the practice is increasingly becoming common at the university level too.
Ao apelar para que seus trabalhos escolares sejam revisados, os estudantes fizeram escola e essa prática está cada vez mais se tornando comum no nível universitário também.

The opposition parties are setting a precedent by abandoning the municipal assembly sessions.

Os partidos de oposição estão criando escola ao abandonar as sessões da assembleia municipal...

Bye!

Here my two cent's worth:

O abandono das sessões das assembleias municipais pelos partidos da oposição está “fazendo escola" na região.

Leaving the City council chambers while in a session/meeting ([1]without permission) is becoming a common practice with opposition parties in the region.

[1] The permission is granted by the presiding officer.

Actually members are allowed to leave, but not in disruptive conduct, to deliberately to obstruct proceeding, change quorum, etc.

Colloquially, it could be "it becoming 'the new fad' in the region".