Google announced that Google Classroom is now available to all G Suite domains including non-profit and business domains. This follows last year's addition of Google Classroom to personal Google accounts. Today's announcement essentially makes Google Classroom available to anyone and any entity that wants to use it.
I wasn't able to turn on Classroom for the business domains that I manage today because this update is on the "extended roll-out" plan. But I'll guess that if this is anything like the other versions of Google Classroom, everyone who participates in a Google Classroom on a business or non-profit domain will need to have a Google account issued by that domain.