As one of the basic skills in 21st century learning, critical thinking (CT) has a positive and key role in undergraduate students' academic achievement and their future professions (Huber, 2016, Snider, 2017). Therefore, it is essential for educators to help learners to develop criticality in different subjects. Recently, studies in ESL / EFL (English as the second or foreign language) classrooms (Chason, et al., 2017; Condon & Kelly-Riley, 2004; Liu, 2018) have also highlighted its significance, whereas some controversy does reside in the adaptability of teaching thinking skills in the EFL context, especially in an Chinese EFL teaching setting. In addition, according to my more than 10 years' EFL teaching experience and related studies (Huang, 1998; Wen and Zhou, 2006), Chinese students' CT performance in writing and public speaking was far from satisfactory.

Although some researchers have testified the effectiveness of integrating CT into EFL subjects (Alnofaie, 2013; Rezaei, et al. 2011; Snider, 2017), these teaching interventions are not always successful (Zare, 2015). No matter what teaching intervention is applied to the teaching of thinking skills, an explicit way is believed to be the most effective. This means it would be better if CT thinking teaching is included within the requirement of a curriculum with a clear teaching purpose and CT strategies. In China, although national EFL English Curriculum Requirement has been revised and has added CT to the teaching objectives in 2020, there is only a general description rather than clear and specific CT teaching objectives. Thus, it is important for practitioners to analyse specific contents of thinking skills based on that general description and to adopt an explicit way in the teaching practice.

Project-based learning (PBL) was expected to be an option to improve students' criticality in EFL classes for the following reasons. On the one hand, it complies with the Chinese government's new requirement, encouraging teachers to use innovative student-centered pedagogy in EFL instead of traditional teacher-centered ones (Ministry of Education of the People's Republic of China, 2016, p.10). More importantly, PBL is more effective in fostering students to think critically than the traditional teaching approaches in tertiary EFL classrooms (Handhika, et al., 2018; Kavlu, 2017).

Based on the above statements, the aim of this research was to explore the applicability and effectiveness of PBL in English teaching to develop undergraduates' critical thinking. Correspondingly, the objectives of this research were to identify if undergraduate students’ CT improve after PBL, to explore how CT instructions in PBL affect students' improvement in thinking, and finally to investigate their attitudes towards effectiveness of PBL to improve CT. The research questions are:

Q1. What is the impact of PBL on EFL students' CT development in Chinese higher education?

Q2. How CT Instructions in PBL might impact the development of EFL students' CT ?

Q3. What are EFL students' attitudes towards and perceptions of the effectiveness of PBL to improve CT?

Adapted from a 10-step model of developing a project in a language classroom (Alan and Stoller, 2005), the framework in this research consisted of 5 stages: pre-project, preparation, implementation, presentation and post-project stage. With a clear CT development teaching purpose, three explicit CT strategies (thinking maps, group discussion and peer review) were embedded into the preparation and implementation stage. This revised CT-oriented PBL teaching framework was expected to help students improve criticality in the context of Chinese EFL teaching. Considering the reality of students' poor CT performance in writing and feasibility of projects' implementation, the form of projects concentrated on writing with different topics according to different units of the textbook.

Case study research design was developed to investigate and interpret the relationships between PBL teaching and students' CT improvement in a Chinese EFL setting. Two 'what' questions were to explore to what extent students' thinking improved after PBL and their attitudes towards PBL and CT strategies. Rich data (CT tests and questionnaires) was to answer the exploratory questions. Additionally, one 'how' question was to explain the dynamic development in the PBL teaching process. Rich and in-depth data (students' compositions and interview) was collected and analysed to respond to the explanatory question. Based on the convenience sampling principle, 94 participants were selected from two classes of the same university with the same major. They were first-year students receiving PBL teaching by the same teacher, who was also the researcher in the study. In such a case study, mixed methods are used to look both holistically and in close detail at the research subjects' CT performance and perspectives of PBL teaching. Quantitative data was to describe the general changes of their thinking through CT tests and overall attitudes through questionnaire. Qualitative data was to gain students' detailed information in thinking performance by their writing and typical personal experience by interview. In brief, before PBL teaching , quantitative data was collected from the California Critical Thinking Skills Test (CCTST) and the California Critical Thinking Disposition Inventory (CCTDI). During PBL teaching, qualitative data was collected from students' writing. After PBL teaching, quantitative data from CCTST and CCTDI, PBL and CT strategies questionnaires, and the qualitative data was from interview. Until now, I have completed the quantitative data analysis of CT tests (paired sample t-test) and questionnaires (statistical analysis). The qualitative data analysis would be completed in the coming months.

Obtained results - CCTST (CT skills): 1. The overall scores before and after PBL intervention increased significantly, but both scores remained at the same Strong assessment level. The result is consistent with participants' potential for academic success and career development. 2. Significantly higher than the mean score of the sub-skill of Analysis before PBL, the score after PBL had reached the Strong assessment level from Moderate level. The result indicates participants' analytical skills have improved. 3. Compare other sub-skills, Evaluation skill achieved the greatest improvement after PBL, but it was still at the Moderate level. This result reveals that participants' evaluative skill have improved significantly, but the assessment level was still at the middle range. - CCTDI (CT dispositions) 1. Students have the strongest CT mindset in Inquisitiveness and weakest mindset in Truth-seeking before and after PBL; 2. Students made the most significant improvement in the disposition of Confidence in Reasoning after PBL intervention. - A PBL questionnaire: 67% students agreed and strongly agreed that PBL teaching could improve critical thinking. - A CT strategies questionnaire 1. Students held positive attitude towards the CT strategies to improve CT, especially in the dimension of CT skills; 2. Although students held strong positive attitudes towards all three CT strategies, thinking maps was thought to be the most effective one. Expected Results - Students' writing: It is expected to have detailed evidence in students' writing to show their CT skills improvement. - Interview: 1. It is expected to gain a deep understanding of how three CT strategies have impacted on students' CT improvement while completing their writing projects. 2. It is also expected to explore students' experience of developing CT by PBL approach.

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