America's school kids do quite poorly when compared against other countries in regards to their level of intelligence demonstrated by standardized tests, even though, America spends an incredible amount of money per pupil and is by far the richest country in the world by aggregate GDP. While there are numerous reasons and theories why America does so poorly, perhaps one of the most compelling reasons comes down to good or corrective vision.
The bottom line is that if you are unable to discern what is written on the blackboard, are unable to read clearly what is it in front of you, you as a student, are dealing with a handicap, especially in comparison to children that have good vision and/or corrective lenses to achieve good vision. While different States have different directives when it comes to vision, this is an area of healthcare, that if necessary, the Federal government has a compelling interest to step in and rectify. While it is one thing to verify the health and inoculations of students, there aren't very many things more important though in regards to a child's potential for engagement and success, than good vision.
For instance, a study as reported by the book "Think Like a Freak" which was done in a poor province of China, in Gansu, in which fourth though six graders were tested for the need for eyeglasses and thereby half of those students who needed eyeglasses were given them and other half continued along without them, to which, the result was that "their test scores showed they’d learned 25 to 50 percent more than their uncorrected peers." According to cbs.nl, the percentage of Americans wearing eyeglasses in 2012 aged 4-12 years was approximately 10%, however, for ages 20-30, that percentage was approximately 40%. This enormous increase in the need for eyeglasses would strongly imply either one or two things: that as we age our vision gets worse and worse, or that children, because primarily they are children, are typically prescribed glasses well after the time that they actually need them, because adults don't feel that children being so young should need them.
There are many theories and things that are considered each and every year to help improve test scores and learning for our K-12th grade students, but could it be that one of the very best things, fairly easy to accomplish, is to thoroughly check the vision of each student and for those students needing corrective lenses, providing eyeglasses free of charge or heavily subsidized to them, based on the income levels of their parents. The sheer amount and masses of money that is already thrown at trying to fix test scores that have been stagnant or regressed over the last few decades, needs just about every valid idea, explored and executed.
While there are myriad reasons why students lose interest in a given subject, most of that lost can be attributed to a form of giving up by that student, to which, if you can't see things correctly or easily, this would be a distinct reason why some students do lose their focus at school.