maybe there is a special term but this is basically it

Skrift comes from skriban = scriptures (see reference) but I think we would say Bible School.

The problem is perhaps more with "gången" (graduate?, passed?)

See what others says. This is just a summary answer

Skriftskola refers to the mandatory catechism ("confirmation class") before the actual confirmation service. In practice, the meaning of the term is a "confirmed member" of the evangelical lutheran church (or, literally, a church member who has attended the mandatory catechism before confirmation).

Is your text FinnishSwedish? A search on 'skriftskolan' gets a lot of Finnish hits for various congregations/churches. This first reference (https://www.esboforsamlingar.fi/livets-fester/konfirmation ) 'confirms' the connection between your term and the religious sacrament. You can surf the Finnish churches website for some info -- conveniently in Swe and Eng, as below (and Finnish if you want!).

I found more hits for 'full member,' which is how I remember this was discussed in the US (100 years ago) as opposed to 'confirmed member.' Here is an example of how my suggestion is used - http://www.bbc.co.uk/religion/religions/christianity/ritesri...