Final answer:
The Institute of Management Accountants (IMA) is the primary professional organization for management accountants in the United States, offering professional development and networking opportunities.
Step-by-step explanation:
The primary professional organization that supports the growth and professionalism of management accounting practices in the United States is the Institute of Management Accountants (IMA). Unlike the International City/County Management Association (ICMA), which focuses primarily on local government leaders worldwide, the IMA specifically provides a platform for management accountants to enhance their professional skills, offers certification programs like the Certified Management Accountant (CMA), and fosters a network of professionals in the field of management accounting. This organization is crucial in the development and advancement of the standards and practices in management accounting, providing members with extensive resources, research, and content loaded with expertise to propel their careers forward.