It's a very odd sentence. I have to wonder if it's something anyone would ever actually say in Spanish, or if it's just formulated to teach translation. Duolingo seems to have a lot of sentences that are peculiar in English -- I'm not sure what context anyone would say something like this. I could understand, "Ellas van a aprender leer," but this sentence seems to imply either that they don't currently know how to read and are going to learn it in the future (then why not use aprender?), or you're telling someone a group of people one is expecting in the future is already able to read. I could only see that if someone needs to be reassured that the 'they' in question will be able to read something. In either case, it's still peculiar.
Ian....here is a possible context. I am a teacher of English as a second language. When discussing my students I could be talking in general about them in the future after I have been teaching them for awhile. "They are going to know how to read."
In reality I would probably say something like "They are going to be able to read English at the 8th grade level."