A Study On The Development Of Written English Complexity Of Senior High School Students

English writing,as an important indicator for assessing English learners' language proficiency,its quality is influenced by many factors.Among them,vocabulary and syntax have attracted much attention from researchers at home and abroad.Based on previous studies and the Theory of Dynamic System put forward by de Bot et al.(2007),this thesis took students from a senior high school in Chongqing as participants in an investigation to explore their development of vocabulary and syntactic complexity in English writing.The thesis tried to find answers to the following questions:1)How does lexical complexity in written English of students develop from Grade10 to Grade 12 in senior high school?2)How does syntactic complexity in written English of students develop from Grade10 to Grade 12 in senior high school?3)Do lexical complexity and syntactic complexity have correlations with writing performance?The results revealed that:1)The development of vocabulary complexity in students' writing is mostly embodied in terms of complexity of words.It has a trend to develop year by year,but vocabulary diversity and density almost stayed unchanged.2)The development of syntactic complexity among students in those three grades is mainly reflected in the change of their unit length of output.It decreases firstly but increases next.The degree of subordination and the complexity of phrase increase just slightly in high school period,and the increase is not statistically significant.3)On the first level,both lexical complexity and syntactic complexity have a significant correlation with writing performance.However,on the sub-level,among the three dimensions of lexical complexity,only the lexical diversity has a negative correlation with writing performance,while neither of the other two dimensions has significant correlation with it.Among the three dimensions of syntactic complexity,there is a simply slight correlation between the length of output unit and writing achievement,which actually decreases with students' advance of their grade.The degree ofsubordination has an extremely low correlation with students' writing achievement in the first two grades of senior high school and their correlation tends to decrease with their grade.Besides,there is a low positive correlation between the phrase complexity and writing achievement just in the first grade of senior high school.