This research study examined the impact of professional development on teachers' performance in Abu Dhabi in the United Arab Emirates (UAE) Cycle Two and Three private schools. The study employed a mixed-method research design developed in two phases which considered professional development (PD) for teachers from the combined perspectives of Adult Learning Theory and Desimone's PD features. The quantitative findings of the research suggest that teachers improved their lesson planning, teaching methods, teaching tools, classroom management, and cooperation after the PD. However, the qualitative findings suggest that teachers had many concerns regarding the current PD program; thus, two features are added to Desimone's framework especially if it is to be used in a country like the UAE.