The goal of Halliwick is independence and is demonstrated as controlled movement. When in water, balance requires adaptation to the mechanical changes in the environment. The adaptations are the result of a psycho-sensory motor learning process. This process that enables the individual to learn how to maintain balance in an unstable environment. Once balance (stability) is established, movement can be initiated and controlled.

McMillan understood the relationship between balance and movement. He realized that in order for children with neurological impairments (e.g., problems with coordination, comprehension, perception and/or pain) to learn to swim (initiate and control movement), they must first learn to balance. Establishing and maintaining balance was not simple, and often impossible, for the children. His response was to develop manual assistance techniques (handling techniques) that would enable the students to learn control of rotational patterns. Based on his observations, McMillan suggested that there was a relationship between fluidmechanical effects and adaptive body mechanics related to inertia, which in many cases, coincided with "primitive reflexes". McMillan accepted the notion of "primitive reflexes" while others were embracing different views of motor learning (e.g., Bobath).

It was not until later that neurophysiology understood the significance of handling techniques as exteroceptive cues or plasticity. Similarly, it is widely accepted that the physical properties of any environment are a major constraint to balance and that individuals show adaptive motor behavior as (e.g., widening the base of support, using hand for support and stiffening the body in order to stabilize the center of gravity) (Carr & Shepherd, 1998). These adaptive motor behaviors (also referred to as stress behaviors) are consistent with McMillan's notion of "primitive reflexes".J. Lambeck,; in "The Halliwick Concept", published in J. of Aquatic Physical Therapy, 8, 2000.