"One's primary classroom" refers to the main place where someone learns and gains knowledge, usually referring to the school or educational institution where they begin their education. Full definition
Likewise, I've experienced some highly effective practices in primary classrooms that would be difficult to implement in secondary settings. (edutopia.org)
She is an experienced primary classroom teacher with a specific interest in mathematics. (cognitioneducation.com)
All the activities include use of simple resources, which can already be found in the typical primary classroom. (educationworld.com)