We know we're not alone when we lament over the iPhone's wonky Autocorrect feature. In fact, there is an entire blog (with a pending book!) dedicated to documenting the strange, sadistic, and silly corrections that the iPhone automatically generates for whatever reason. Thankfully, we found the only way to finally end the pesky issue so your iPhone will no longer incorrectly autocorrect.
Most of us by now know the Autocorrect feature is "intelligent" and apparently "learns" what words you type frequently and will remember them in its memory. But no matter how many times we hit that tiny "x" after the suggested word appears, it never seemed to learn the difference. In our case, the most recent (and annoying!) offender was the iPhone autocorrecting "as" to "A's". I'm sure you can imagine how maddening that could get very quickly.
Curiously, the only way to permanently make the iPhone "learn" the specific words and not autocorrect them is to type them while using Safari (people tend to use the Google Search Bar for simplicity's sake). For whatever reason, performing the same task in other Apps won't make the iPhone "learn" the word. So, once you're in Safari, begin typing the troublesome word and once the suggestion appears, hit the "x". Do this about 3 more times and the iPhone should finally learn the new word.
And of course, you can put the kibosh on the entire Autocorrect function by accessing "Settings/Keyboard/Auto-Correction: OFF"