Using a low inference observation instrument, we investigated the effect of an ongoing, intensive, and structured virtual professional development [VPD] on fidelity of implementation across conditions in a randomized control trial validation study implemented in seven Texas school districts. The observations were collected three time in the beginning, middle and the end of school year. The results indicated that VPD had statistically significant impact on teachers' fidelity of implementation. Experimental teachers overperformed teachers in control condition in student involvement, level questioning, applying ESL strategies, providing affective and cognitive feedback, and more English material to encourage ELLs participated in classroom activities.