Union apprenticeship sign-ups near Baltimore

I heard of an apprenticeship with paid on-the-job training for people changing careers. I am in Baltimore, in case local advice matters. Classes are in the evening and work is during the day. Did anyone go through it?

You earn while you learn, but the first year is tight. Plan your budget carefully.

The aptitude test was mostly maths and reading a diagram. Free practice tests online were enough for me.