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What support and education are you able to give them - will you need to acquire additional study help? If so, you may want to contact the government agency; and get either a tutor, counsellor (yes, times may get hard!), or school coordinator.
Has your teenager finished high school or are they doing this as well/instead? Your teenagers teachers may be able to help you - or put you in touch.
They might also be able to recommend some books and study guides.
If it was me, id want to be equipping them with the best education possible. So branching out on all the different avenues; contacting staff, teachers, counsellors, etc. Purchasing books (exercise book, dictionary, etc) and ensuring they have a comfortable workstation.
Are they motivated? Together, it can be a bit of a struggle - yet rewarding experience (as said above!). :)