Toilet-training expert Jamie Glowacki’s self-published OH CRAP! POTTY TRAINING has sold more than 40,000 copies and has been the “dirty little secret” of moms on message boards and in parenting groups for years.

Now, this proven, 6-step plan (called “the WHAT TO EXPECT of potty training books” for its comprehensive, no-nonsense voice) is available to the...