No. A refresher course would be to remind, to make new those things which you had once learned. For example, those who know CPR need to take a refresher course every few years to make sure they remember. Or if you are in charge of safety at an industrial plant, you would train all new employees in safety procedures, but you would also have all employees take refresher courses every year or two.
Remedial is to teach things to those who have never learned them, but should have. For instance, some colleges have to offer "remedial math" to students who have managed to graduate from high school without obtaining the proper skills to succeed in college.
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