I remember being assigned Buchan's "Thirty-nine Steps" for a report on suspense writing. A fine book, still in print.

Henty, of course, would seem out of date to modern youth, much as the "Tom Swift and ...." books are.
Even "Terry and the Pirates;" recently issued is a prime 6-volume edition of this graphic story of the 1930s-WW2 using Ohio State archival Milton Caniff material; is dated and brings yawns and perhaps giggles to kids nowadays, but it is invaluable to adults interested in what people thought during that period.