Nowadays, technologies are highly developed and engaged in almost all human activities. The mobile applications used for many kinds of purposes and have become a common part of our daily activities. The learning process of the young generation today is important to go with technologies that became the ordinary knowledge of their daily life (Kostrzewski, 2012). This kind of process hopes to create a significant motivational aspect to the students and leads them to the effective learning process both in the formal school and informal learning area. For these reasons E-learning increasingly used in formal and informal school or even in a college degree. The online learning is an excellent opportunity to learn because it creates a suitable, enjoyable and entertaining learning environment, which creates a positive mood to the learner (Mason & Rennie, 2006).

TOEFL is one of the standardized tests which have applied by institutions and universities all around the world to test the English language ability or skills of their students. It also becomes one requirements of the registration or even graduations in some college degree for the students. However, several students encountered the difficulty in answering the TOEFL in section two which present them with the Structure and Written Expression.

This paper is mainly focused on research examines how the use of mobile educational Duolingo application in teaching TOEFL preparation of structure and written expression. It also discusses the encouragements of the learner’s motivation and understanding through the process of learning in the classroom and home environment. Duolingo application, which enables free online language learning.

Duolingo explored, considered and tested in terms of appropriateness and quality of an educational application tool in the classroom. The goal of this paper first is to know the effectiveness Duolingo in teaching TOEFL preparation of structure and written expression on twelfth grade. Second is to know the learner’s response to the application. The third is to examine the student’s motivational impact from the use of Duolingo. The research findings hope to assist foreign languages teachers and students who take part in foreign languages courses which combining the use mobile learning educational application in their process of learning.

There are researchers that explain the effectiveness of mobile technologies which can help and improve student in language learning skills, especially in learning structure text. Mobile technologies know gives the students to have high usability on learning, be easy and simple to work with and some observe that mobile technology improve the satisfaction and desire to learn useful (Viberg & Gronlund, 2013). They also found that the disadvantages of the mobile device for learning are the small keypad and the screen of mobile devices. It also very dependence on the use of the internet.

The other previous research conducted by Norshahila Ibrahim, Wan Fatimah Wan Ahmad, and A’fza Shafie (2016) about the Effectiveness Study on Multimedia Mobile Application for Children: Mfolktales Application, University of Sultan Idris, Tanjung Malim, Perak, Malaysia. Their research paper discusses the effectiveness testing for MFolktales Application to measure effectiveness level in students’ comprehension performance after using the MFolktales mobile application. It has a significant improvement in the Experimental group so MFolktales application can be considered as effective.

There is a lot of Applications in Mobile devices focuses on Education accessible by free of even premium on the internet. This research paper focuses on examines the effectiveness of one of that MALL namely Duolingo. The researcher uses this application in teaching the preparation of section two in TOEFL which focuses only on practicing the student’s written expression and structure. It examined how the process of language learning through the application of Duolingo recognized by the students, and which aspects and features in this application that motivate them to use it more in their language learning process. To understand the Duolingo effectiveness, three research questions were presented.