Primary programming is a stage of Transformer development that seems to be somewhat akin to Elementary school for humans. Though little detail has been revealed about it, we know that newly created Transformers enter primary programming along with their "classmates" to learn the basics of functioning in society. Upon graduation, Transformers are considered ready to take up their function, though they may still be quite young and immature.
All mentions of attending Primary programming thus far have been in relation to mini-cons. It is unknown if non-mini-con Transformers also attend.