This paper reports on Ecuadorian pre-service and in-service teachers' ability to conduct action research in the classroom as well as their skills to efficiently adjust instruction to address students' cultural and linguistic diversity. A qualitative case study approach was implemented to collect information from teacher candidates in 2015, in-service teachers from a public school in 2017, and in-service teachers from a private school in 2019. Data were collected through focus groups and interviews conducted in Spanish. Findings suggest that training teachers to conduct action research will improve their ability to analyze data and improve students' learning outcomes.