With the advent of numerous newly-published English course books, textbook evaluation has turned into a very critical area in English Language Teaching (ELT). This paper aims to evaluate the English textbooks being taught in Iranian Junior high school ("Prospect" series). In so doing, an evaluation questionnaire was distributed among 27 female and 42 male junior high school teachers. Having collected the survey data, in order to obtain a richer understanding of teachers' opinions, follow-up interviews were conducted with 11 teachers. The results indicate that although "Prospect" series can be considered a breakthrough in comparison to the previous English textbooks, they suffer from some critical shortcomings in terms of activities, methodology, topics, design, and insufficiency of teaching hours. Overall, the findings suggested that the textbooks fell short of Iranian teachers' expectations and need critical improvements to reach their bests. Results of the present study have implications both for English material developers and curriculum planners.