This study aims to determine in-service training needs of novice and professionally experienced social studies teachers regarding the planning, implementation and assessment processes of project tasks. The study was carried out using comparative case study from qualitative research patterns as base. Eight social studies teachers who were determined by means of extreme and deviant case sampling constitute the participants of the study. Interview method was used in data collection and collected data were analyzed with inductive content analysis approach. As a result of analysis, it was determined that social studies teachers need an in-service training that includes basic features of project based learning approach and context-based practices. In addition, it was found that teachers need to improve their knowledge and skills especially concerning "taking student and curriculum characteristics into consideration in project processes," "adaptation of project processes into different education environments" and "development and usage of objective assessment tools."