To add, everyone likes to live up to their expectations from people around them. If you think Jane needs help with her English, recall her last achievement and bring it up, "Hey Jane, I think you did a great job on punctuation last week. I am sure you will handle the extempore discussion well too this Friday. Let me know if you need any help!"
This way, Jane would be confident that as she has already proven her abilities in English punctuation [she knows now that she can learn and can be good at it too], she can do well in other areas in the language too. Moreover her teacher expects her to do well so she must live up to that expectation.