Transition assessment is a required component of transition services for students with disabilities according to IDEA.
Transition services. Beginning not later than the first IEP to be in effect when the child turns 16, or younger if determined appropriate by the IEP Team, and updated annually, thereafter, the IEP must include—
(1) Appropriate measurable postsecondary goals based upon age appropriate transition assessments related to training, education, employment, and, where appropriate, independent living skills
IDEA 2004 §300.320
Education and Training Assessments
Independent Living Assessments
Healthcare and Medical Assessments for Transition