Saccades are the very quick eye movements your eye make when you are reading. They happen over an incredibly short time at very high speeds. Your eyes dart from word to word, quickly stopping (fixating) and then continuing onward.
Saccades and fixations are types of eye movement. The spatial-temporal sampling of the ability of the human eye, demonstrates the way in which we take in the information we are receiving about the world through our vision. This includes it’s limits. As such, it is useful to study not only the properties of the eye, but it’s movements, and that is where these terminologies are derived from.
Fixations are periods where the eye or eyes are more or less still, and saccades are periods of rapid eye movement between fixation points.
In order to read, it is necessary for the eyes to maintain proper convergence. When they don't, a person with convergence insufficiency may be able to read without initial problems, but quickly become tired, get double vision, get blurry vision, or have headaches.
If you or your child is having difficulty reading, there are many ways to improve reading skills. First, get a full vision exam. That may reveal problems caused by underlying vision issues. Once you confirm it is or is not a vision issue, you should make sure you have good lighting, have proper glasses, and practice reading regularly.