A teacher may pursue additional degrees in education or her content area. Consequently, her students gain a teacher with refined instructional skill and/or a greater degree of expertise in her field.
School districts commonly offer continuing education on a particular topic or strategy. Studies have shown this kind of training to be disconnected from actual curriculum and to have little effect on student achievement.
A new trend in continuing teacher education involves educators in a series of ongoing discussions---based in research and practice---which specifically address topics related to curriculum and instruction. This produces dramatic gains in student achievement.
A teacher who seeks additional training from outside of his school district can expect to see the same effect as if he had taken the same training within his district.
Regardless of the other circumstances, a teacher who purposes to benefit from any training opportunity will see better instruction and better learning; a teacher who is disengaged from training will gain no benefit for herself or her students.