With the increase of reading measure, teachers began to become more aware of the students’ reading problems. This brought on the search for the factors that enabled children to be “prepared mentally” for reading. Reading readiness refers to the skills that children develop that guide them towards reading. From the 1920s-1950s, reading readiness was thought to be a product of maturation. Around the 1950s until the 1960s, reading readiness changed to be thought as a product of experience. During the period of reading readiness as a means of maturation, teachers believed that students were ready to read once they reached the mental age of 6 years and 6 months. Teachers would closely monitor their students to determine when each child was mentally ready to read. During this period reading readiness workbooks and assessments became popular.