There is no boredom (not even an invalid's) comparable to that of a boy who has nothing to do...writes the great Pulitzer Prize-winning novelist Booth Tarkington in his book "Penrod and Sam." When adults of the parental kind have plans and chores and schedules, an 11-year-old boy's life is dull and unexciting. But when these boys have opportunities for dubious experiments or neighborhood skirmishes with other children or travels of discovery, adults pull back on the reins and check any impulsive advances. And yet Penrod Schofield and Sam Williams are still able to prove their inventiveness and ability to sustain any exploit that may have tantalizing results. Such situations include rescuing an old and hard-worked horse, chasing black snakes, feigning sickness to avoid school, and saving an unsympathetic cat from drowning. Thinking they're going to find out their children's feelings and activities, parents ask politely vague questions and get nonreflective one-syllable answers. Then when grownups ask more direct questions intended for investigation of specific events, young boys mutter and evade as if deaf. Tarkington's talent for describing circumstances from a boy's perspective almost makes this book a manual that defines a youngster's responses to his confusing and bewildering existence.