The research only measured the short-term effects of instruction. There is no way of knowing whether instruction had only permanent or long-term effects on learners’ developing interlanguage systems. Clear instruction may lead to more positive results, especially if the instruction consists of contrastive information about first language and second language “Teach what is teachable” proposal has an important role for syllabus planners as well as teachers.
The research also shows that instruction on language that is ‘too advanced’ may still be helpful by providing learners with samples of language that they will be able to incorporate into their interlanguage when the time is right.