The plain language of the ADA covers discrimination on the basis of disability during job training. 42 USC 12112(a)("No covered entity shall discriminate against a qualified individual on the basis of disability in regard to job application procedures, the hiring, advancement, or discharge of employees, employee compensation, job training, and other terms, conditions, and privileges of employment."). The coverage provisions include this expansive list, extending beyond recognized traditional employment activities, to prevent periods -- including training periods -- during which discrimination might be undertaken with impunity. Thus, the statutory inclusion of "job training" protects individuals while they receive the training required to perform the essential functions of their ultimate job position; it protects them from discrimination that could deny them the means to obtain qualifications necessary to undertake that position. It cannot be disputed that the ADA covers individuals in training without regard to whether they are called employees, conditionally-hired employees, trainees, or a title specific to one employer.
Read more about this rule and the ADA at Robert Abell's Kentucky Employment Law Blog: ADA Applies During Job Training; Is Psychological Counselling A Medical Examination Under the ADA?; Damages For Pain and Suffering Caused By Employer's Refusal To Accomodate Disability; Is Driving A Major Life Activity Under the ADA?