cienie-isengardu:

Clones who showed early initiative and leadership abilities were singled out for enhanced programming and officer training.

On other hand, clones who proved deficient or had undesirable mutations were reconditioned – a term that included everything from genetic therapy to termination (After the Jedi took a more active role overseeing clone trooper training, terminations were largely halted, with deficient clones shunted into support roles).

(source: Essential Guide to Warfare)