The problem, as I see it, of basing a curriculum around the order of acquisition is that the acquisition is based on accurate input of all levels. So, like I've heard again and again since joining the TPRS world, we shelter our vocabulary, not our grammar.
I think we have the name wrong anyway. I was typing a nice paragraph about how if we shelter the grammar then we never acquire the other structures. And I realized, it isn't the order of acquisition at all! It's the order of output!
I have two boys, the older one is three and the younger one is 20 months. Let me tell you, they understand and have acquired waaaaayyyyyy more than they can output. My three year old has an amazing grasp of language and uses every tense accurately. Last night, however, he said something about his two foots. Now, when he hears an adult say "foots" he knows it's wrong. But, in the hurry of getting his thoughts out quickly, it came out wrong. Which is perfectly normal.
I think the most valuable piece of understanding the order of acquisition is that we can understand why our students keep making the same mistakes, even though we've gone over the correct version ad nauseum, and we can loosely judge where students are in their acquisition of the target language.
4 hours ago