There are numerous changes to the novel, including: reducing Valjean's prison term to 10 years (1800-1810) instead of 19 (1796-1815), abridging the ordeals of Fantine (probably to conform to Hays Office Code), having Cosette learn Valjean's true identity at the start, changing the backstory of Eponine from street urchin to secretary, and stating the students' goal to be law reform rather than overthrow of the government. The streetwise little boy Gavroche, a popular character from the novel, is not shown at all.
This was Fox's production head Darryl F. Zanuck's attempt to beat MGM at its own game. MGM had scored several successes with adaptations of literary classics like David Copperfield (1935) and Little Women (1933) under the aegis of wunderkind producer David O. Selznick. This also afforded Zanuck the opportunity to provide his latest star, Fredric March, with a high-class production.