Since reading is a skill, the very act of doing so produces some improvement even if done in a non-attentive manner. Of course, the degree to which one improves is certainly mitigated by the lack of thinking that accompanies the reading. However, it has been proven that if students are made to read and they actually exercise this movement of the eyes on pages, usually many will begin to pay attention to what they are doing and, thus, develop some skills.
One recalcitrant student in a particular high school was in a class in which specific times were set aside for reading. Since the majority was complying, he,too, began to read and eventually found himself engrossed in the book. Later, he wrote that he had never read an entire book before, but he knew now why people enjoyed reading. He continued to read and his literary scores did improve.