This study was based on the research which attempted to investigate portfolio as an assessment instrument for students’ writing skill of procedure text. The main purpose of the study was to find out how effective is portfolio as an assessment instrument for students’ writing skill of procedure text.
The method of the research was experimental study. Data were obtained by giving test to the experimental class and control class after giving a different treatment to both classes. The experimental class was asked to write procedure text and assessment by using portfolio, while the control class was asked to write procedure text only. The subject of the research was 92 students. Two classes were selected randomly by the process of simple random sampling, they were class X D ( 46 students ) as experimental class and class X A as control class ( the students who were not assessed by using portfolio ).
The instrument that were used to collect the data were classroom test. The test was used to know students’ competence before and after the experiment was run. There were two kinds of test. They were pre-test and post-test. The kind of test were writing test.
The mean of writing score of experimental class ( assessed by using portfolio) was 79.70 and the mean of writing score of control class ( the students assessed by using non-portfolio ) was 76.93. There was a significant difference in writing procedure text score between students assessed by using portfolio and those who are not. It was showed by the mean of experimental class was higher than control class. On the other hand, the test of hypothesis using t-test formula showed the t-value was higher than the t-table. The score t-value was 1.94, while t-table on = 5% with df 90 was 1.66 ( 1.94>1.66). So, the hypothesis was accepted.
Based on the results of the research, it could be concluded that portfolio as an assessment instrument is effective for students’ writing skill of procedure text. It helped the students solve their problems in writing procedure text and improve students’ writing class.