In the crowded field of toilet-training books, Alona Frankel’s Once upon a Potty, first published in Hebrew in 1975, has become something of a classic. Frankel’s homespun illustrations, clean design, and simple text have stood the test of time, and the book (both boy and girl versions) is still popular today — maybe because those kids who first trained with Joshua and Prudence are now helping their own children get a handle on the potty.

Oceanhouse Media’s Once upon a Potty app (June 2011) is true to the original. The focus is on the text and illustrations; digital enhancements are used sparingly and effectively. There are some polite potty sound effects and humor, and though I’m sure the urge was strong (get it?!) to make more of a splash (it’s too easy!), the producers wisely kept the intended audience in mind. The narrative’s reassuring tone, nonthreatening pictures, and unobtrusive music help easily distracted toddlers focus on the important information.

My test subject (male, age 3) has looked at a bunch of potty books over the last year or so, but we haven’t read Once upon a Potty. Personally, I don’t care for Joshua and Prudence. Well, they’re okay, but the text in their books is long and strikes me as condescending. Plus, the illustrations are so 70s, and not, I think, in a hip way. These were not distractions, it turned out, for my test subject (nor was reading the girl version).

We chose to be read to (by a pleasant, unhurried reader), turning the “pages” ourselves. My tester sat in rapt attention through the whole thing, listening and absorbing facts about Prudence’s body parts and functions. The narrator took her own sweet time getting through the story — good for a three-year-old in the throes of figuring out this developmental milestone.

I really liked being able to watch and listen to the story on the hand-held iPad; I don't think watching this particular DVD on television would have had the same impact. The only real problem I encountered — and it’s not much of one — was that by being read to, I couldn’t change “a pee pee for making Wee Wee” and “Poo Poo” to terms we use at home. But that’s easy enough to comment on before the next page turn.

OM’s version offers the standard app options: in addition to being read to, you can choose to read the text yourself or use auto play (where text and page turns happen, er, automatically). There’s also a cheesy “Potty Song,” which my tester thankfully had no interest in. If I had to sing "The Potty Song” on demand all day, I might just have to stick my head in the potty and flush.

Potty on.

Available for iPhone, iPad, and iPod touch (requires iOS 5.0 or later) in girl and boy versions as well as for Android devices (girl and boy); $1.99. Recommended for preschool users.