Mrs. Ashford has finally taught the last of the five short vowel sounds and is delighted to move on to teaching the long vowels. She teaches long a to mastery before moving on to the long i sound. During the next two weeks, as she teaches the students words with long i, Mrs. Ashford doesn't have students read any words with other vowel sounds besides the long i in order to avoid confusing them. Every day the students read only words with long i. What instructional enhancement is Mrs. Ashford violating by not continuing to provide ongoing practice reading vowel sounds that the students learned in earlier lessons?