Training of horses involves a balance of trust and dominance between animal and trainer. Yet in a herd, horses will establish a social hierarchy, which lends to antagonistic behaviors. The objective of this research was to characterize behavior and interactions between horses and determine the implications on the trainability of the horse by trainers of varying skill levels. To accomplish this test, horses (n = 10) from the Sam Houston State University behavior and training course were randomly selected and individually introduced in 9.14-m round pens to control horses (n = 5) over a 2-wk period. The interaction between the horses was recorded by 3 independent observers and scored on a 15 cm line scale ranging from submissive (1) to aggressive (15). Horses were individually worked by one of 5 trainers of varying skill levels. Activities included ground work only, and maneuvers began with haltering and leading to advanced maneuvering through obstacle courses. Horses were blindly scored by the same 3 observers using a 15 cm line scale ranging from obedient (1) to resistant (15). Horses were then placed into 2 groups (Difficult, Easy) based on average difficulty of training, and the aggression scores were compared across the 2 groups using the PROC GLM procedure in SAS 9.2. Correlations were calculated between the average aggression and training scores for all test horses. Results from the training scores showed a difference (P < 0.01) between the 2 selected groups, indicating that the separation of the groups was valid. However, no difference was detected (P = 0.22) in aggression scores between the Difficult and Easy training groups. This illustrates that the aggression of a horse in a herd or in establishing a social order may not be a good indicator of the difficultly to subsequently train the horse. This is further demonstrated in the weak correlation (r = 0.408) between the average aggression and training scores for the test horses. While in establishing social order aggression may be observed, but it is not the sole factor in determining dominance in a herd. Most likely the trait of dominance may be more important in terms of trainability than aggression and should be the focus of future behavior research.