Any RLS should be very engaging. Treasure Island is the classic, but I'm a minority opinion for Kidnapped. The sequel, Catriona (or David Balfour in America) is a political thriller and probably too deep, as well as having an entire chapter in the thickest of Lothian dialect.
Kipling's later stories are too tough (and the themes too adult) for junior high, but his Jungle Book and some of the Plain Tales would be perfect. I would even give the kids a shot at Beowulf in a modern translation, and the boys should eat Fagles' translation of the Iliad up (in metered doses).
And before you say I'm being unrealistic, I taught a unit on Greek history to my daughter's 7th grade history class. The kids memorized the first six lines of the Iliad in Greek, and we chanted them (a hobby of my first Greek teacher, who also had some odd theories about pronunciation) . . . then we looked at several very different translations and discussed the compromises made by translators. We talked about what it was like in the time of Homer's heroes, and how they were about as far from the Greeks of Classical Athens as we are from the Norman Conquest. Talked about Heinrich Schliemann and his belief that the story of the Iliad was real, and how he went about proving it . . . passed around replicas of the Mask of Agamemnon and a Bronze Age sword (boys loved that), then we dressed up in Greek attire and ate baklava.
They had a ball.
Is ANYthing written less than 75-100 yrs ago automatically disqualified as good? I read the Potter series, and I really enjoyed it, as did my two oldests (my youngest just started them). I enjoyed the Hunger Games series. Not to be snarky, it just seems this is “one of those topics”...