Sometimes you can find the statistics you need in a journal article, but frequently discipline related statistics are gathered and reported in different formats.
American Association of Christian Schools
American Association of School Administrators
American Educational Research Association
Association for Childhood Education International
International Society for Technology in Education
Music Teachers National Association
National Afterschool Association
National Association for the Education of Young Children
National Association of Biology Teachers
National Association of Elementary School Principals
National Association of Independent Schools
National Association of School Nurses
National Association of School Psychologists
National Association of Secondary School Principals
National Christian School Association
National Council for the Social Studies
National Council of Teachers of English
National Council of Teachers of Mathematics
National Educator's Association (NEA)
National Middle School Association
National School Boards Association
National Science Teachers Association