Reality: Cognitivist theorist Krashen made the Natural Order hypothesis which is based on research findings (Dulay & Burt, 1974; Fathman, 1975; Makino, 1980 cited in Krashen, 1987) that suggested that the acquisition of grammatical structures follows a 'natural order' which is predictable. This hypothesist suggest for a given language, some grammatical structures tend to be acquired early while others late. The order seems to not be tied to the learners' age, background, external factors, and even though the study was not 100% accurate there were statistically significant similarities that reinforced the existence of a natural order of language acquisition. Theorist Krashen points out that the implication of the natural order hypothesis is not that a language program syllabus should be based on the order found in the studies. In fact, he rejects grammatical sequencing when the goal is language acquisition. "Because the natural order seems to be immune to teaching, drilling a student on a grammatical item before he or she is ready to acquire it will be of little use". (Wright, 2015). In short lock step item mastery is non-beneficial to second language acquisition.
Resources:
Wright, W. (2015.) Instructional Programs for English Language Learners. In Foundations for Teaching English Language Learners: Research, Theory, Policy, and Practice ( Second Ed., pp. 97-111) Phhiladelphia, Pennsalavinia: Carlson Inc.