Concept: For educational planning, learners with mental retardation (intellectual disability) are traditionally classified according to the degree of impairment and the kind of schooling/care they can benefit from. The three recognised educational categories are:
Educable — mild retardation; can acquire basic academic (reading, writing, arithmetic) and vocational skills.
Trainable — moderate retardation; cannot handle academics but can be trained in self-care, social and simple occupational skills.
Custodial — severe/profound retardation; needs lifelong supervision and care rather than instruction.

Why the answer is the odd one out:
'Analytical' is NOT a category of learners with mental retardation at all. It refers to a cognitive/thinking style or a type of ability (analytical intelligence), not a level of intellectual disability. Hence it cannot be used to classify such learners for educational purposes.

Why the others do not fit the 'cannot be categorised' requirement:
Educable, Trainable and Custodial are all genuine, established educational classifications of mental retardation, so each of them CAN categorise the learner — making them incorrect choices for a question asking what does NOT apply.

Takeaway: Educable, Trainable and Custodial are levels of intellectual disability; 'Analytical' is a thinking style and does not belong to this classification.
Correct answer: Analytical