The term stems from a parable recorded in Matthew 25:29 (with the maxim resulting from it that 'the rich get richer, the poor get poorer').
It was used in the scientific field to describe how when two scientists do the same work or research independently, the more known scientist usually gets the credit for it.
In education, the term "Matthew effect" has been adopted by psychologist Keith Stanovich[1] to describe a phenomenon observed in research on how new readers acquire the skills to read:
early success in acquiring reading skills usually leads to later successes in reading as the learner grows,
while
failing to learn to read before the third or fourth year of schooling may be indicative of lifelong problems in learning new skills.
[2]
The reasoning behind this is the following:
During 'Learn to Read' stage
Children who fall behind in reading tend to read less -> increasing the gap between them and their peers.
During 'Read to Learn' stage
Now, the reading difficulty creates difficulty in most other subjects. In this way these children fall further and further behind their peers in other subjects at school, too.
In the words of Stanovich: Slow reading acquisition has cognitive, behavioral, and motivational consequences that slow the development of other cognitive skills and inhibit performance on many academic tasks.
We can also apply the Matthew Effect in sports: a person who is severely overweight and not athletic will find it very difficult to run a marathon. It would be easy for them to give up - whereas for a sporty person, training for a marathon seems not such a daunting task. This is where a personal trainer or coach would step in to help the first person turn the spiral around by giving tasks that are achievable.
With reading, Vision Therapy plays a similar role. It helps bringing children from the downward spiral or not seeing and perceiving images and text clearly into the positive, upward spiral where texts become first manageable and then enjoyable.
This in turn will help to navigate better through school and life.
Sources
[1] https://en.wikipedia.org/wiki/Matthew_effect
[2] http://blog.allaboutlearningpress.com/matthew-effect-in-reading/