The sentence in question is "我觉得留学是一种很好锻炼" Can I use “锻炼” in this context?
If you want to express: I think studying aboard is a good practice, then your Chinese sentence "我觉得留学是一种很好锻炼" doesn't connote the same meaning in my opinion.
"我觉得留学是一种很好锻炼" means "I think studying aboard is a good way to train ourselves." The sentence doesn't specify the areas(willpower, ability to live alone and etc.) on which we can get trained.
Well, "studying aboard is a good practice" is like saying 出国留学是一种很好的实践 in Chinese.
Note that you should add a 的 in your sentence to make it more natural: 我觉得留学是一种很好的锻炼.
锻炼 probably means something different than "good practice" in this context.
Its meaning is closer to "tempering one's willpower" or "psychological training", as well as "improve one's abilities in various subjects".
IMO, "good practice" means "a good way to do something" or "something good to do", both of which are different from ""