The phrase "proficient work" means doing something skillfully and well. It refers to doing a task or job with expertise and being capable and knowledgeable in that particular area. Full definition
This means that they have only partially mastered the knowledge and skills that are fundamental for proficient work at their grade levels. (edweek.org)
Two - thirds meet only the standard for «basic» literacy (a partial mastery of the knowledge and skills considered to be fundamental for proficient work at each grade level). (ciera.org)