the other hand, other studies have shown that if a short summary of the link's content is provided when the mouse pointer hovers over it, then comprehension of the text is improved. "Navigation hints" about which links are most relevant improved comprehension. Finally, the background knowledge of the reader can partially determine the effect hyperlinks have on comprehension. In a study of reading comprehension with subjects who were familiar or unfamiliar with art history, texts which were hyperlinked to one another hierarchically were easier for novices to understand than texts which were hyperlinked semantically. In contrast, those already familiar with the topic understood the content equally well with both types of organization. In interpreting these results, it may be useful to note that the studies mentioned were all performed in closed content environments, not on the internet. That is, the texts used only linked to a predetermined set of other texts which was offline. Furthermore, the participants were explicitly instructed to read on a certain topic in a limited amount of time. Reading text on the internet may not have these constraints. Professional development The National Reading Panel noted that comprehension strategy instruction is difficult for many teachers as well as for students, particularly because they were not taught this way and because it is a demanding task. They suggested that professional development can increase teachers/students willingness to use reading strategies but admitted that much remains to be done in this area. The directed listening and thinking activity is a technique available to teachers to aid students in learning how to un-read and reading comprehension. It is also difficult for students that are new. There is often some debate when considering the relationship between reading fluency and reading comprehension. There is evidence of a direct correlation that fluency and comprehension lead to better understanding of the written material, across all ages. The National Assessment of Educational Progress assessed U.S. student performance in reading at grade 12 from both public and private school population and found that only 37 percent of students had proficient skills. The majority, 72 percent of the students, were only at or above basic skills, and 28 percent of the students were below basic level. See also Balanced literacy Directed listening and thinking activity English as a second or foreign language Fluency Levels-of-processing Phonics Readability Reading Reading for special needs Simple view of reading SQ3R Synthetic phonics