This paper explains the investigative attempts of The New York City Math Exchange Group (MEG) on elementary mathematics teachers' content knowledge in Adult Basic Education (ABE). The study is comparative in nature and took place in a workshop at the Adults Learning Maths Conference in Boston. The new members of the MEG professional development group were compared to the veteran members. It is observed that among the experienced MEG members, the ability to compute a division problem, create story problems, and reason mathematically and abstractly were higher than in other studies of U.S. teachers and the sample of new MEG members. It is concluded that it is only through comprehensive and ongoing staff development that all teachers can better understand, apply, and teach mathematics to their students. (SOE)