Farmer In The Sky is one of 14 "juvenile" science fiction novels written by Robert A. Heinlein (Stranger In A Strange Land, The Puppet Masters, etc.) between 1947 (Rocket Ship Galileo) and 1962 (Podkayne Of Mars). It is not one of the author's best works, but probably the most typical - that is, the best single example of his work, fitting, in more ways than one, right in the middle. Heinlein's juvenile novels are all exceptionally well-written, as entertaining and enlightening for adults as for teenagers, but appropriate for kids to read. Each novel (with a couple exceptions) deals with space exploration in settings that expand on the previous novels - first, the moon, and later on, the stars.
Farmer In The Sky, written in 1950 (and first published as "Satellite Scout" in Boys' Life magazine), was one of Heinlein's last limited to our Solar System, after his characters had explored the Moon, Mars, and Venus, but before moving on to the stars, a step barely hinted at in this novel and the next (Between Planets). It's the story of young Bill Lermer and his widowed father, George, who decides to emigrate to Ganymede, one of the four larger moons of Jupiter. Bill feels abandoned when George remarries apparently because it's a requirement of emigration, but he's determined to stick with the newly restructured family and fly to Ganymede with them. There's plenty of suspense and adventure on the space journey and on the new world.
The author's writing style and depth of characterization is superior to typical juvenile novels like Tom Swift or The Hardy Boys. Heinlein works in appropriate ideas and lessons for young readers, like a character perceived as an irresponsible, inconsiderate jerk at the beginning, who turns out to be a reliable friend by the end, and a few examples of dealing with death and catastrophe, as well as his usual tidbits of philosophy, such as a discussion of population pressure inevitably leading to war (an event realized in the next novel in the series, Between Planets).
I believe this is the first novel ever to seriously explore the concept of terraforming a desolate alien world for human colonization. It is also unique in the skillful marrying of two diverse genres (or at least, settings), the futuristic space adventure and the pioneer farm family (Heinlein was raised on a farm), without changing pace or belying characters. Heinlein revisited that concept in later books like Tunnel In The Sky, but with less contrast.
If you've never read Heinlein, Farmer In The Sky would be a good one to start with, even if not the best. Overall, it's good enough to get 5 stars, for readers of all ages.