When discussing the paper "The Influence of Reading on Vocabulary Growth", the concept of one-sided or two-sided Matthew Effects comes into play. The research study looks at this concept to see how the difference in reading skills that students have can affect later vocabulary growth.

• a one-sided Matthew Effect is when the difference in achievement or variable between two or more groups of students only leads to a significant difference in one group (i.e. a student group of strong readers will show strong increases in vocabulary growth while average and less-skilled readers show similar rates of growth with no influence from the reading skill variable)
• this one-sided effect can also be reversed, in that less-skilled readers show lower rates of vocabulary growth than the average while stronger readers show no particular difference compared to the average