I read this book when I was in elementary and it was a little lost of me, not in the least because Verne almost always have a pedagogical goal, in addition to wanting to tell a roaring good yarn (which he did).
When I read 20,000 Leagues Under the Sea, I was somewhat disappointed in how the desire to educate got in the way of an exciting tale. Journey to the Center of the Earth had no such problem.
Though I will add, though I hope it’s superfluous, that much of the science has been… superseded by more recent discoveries.
If you have primarily seen the various movies (as a kid, I remember one with James Mason and I was inspired to reread the novel by having my daughter watch the surprisingly fun version with Brendan Fraser), you may be surprised by the lack of dinosaurs. There is a fight between a plesiosaur (of some kind) and an ichthyosaur (of some kind), each of a size that I think rather exceeds that of known members of those groups. There is also a herd of mastodons who are, apparently, being herded by a twelve foot high prehistoric man of some kind. Exciting stuff, but not really what I was looking for as a child. This would have been better for me to have tried to read in middle school.
But if you do want dinosaurs and want to stay in this sort of genre, Arthur Conany Doyle, of Sherlock fame, wrote a novel featuring Professor Challenge called The Lost World. Try that one.