The correct answer is: Student achievement level.
Student achievement level is the most important indicator of quality of education in a school because it measures the extent to which students are learning and mastering the material that is being taught. This is important because it indicates whether or not the school is providing a high-quality education that is preparing students for success in college and beyond.
Infrastructural facilities, classroom system, and text-books and teaching-learning material are all important factors that can contribute to student achievement, but they are not as important as student achievement level itself. A school with excellent facilities and resources can still have low student achievement if the teachers are not effective or the curriculum is not well-designed. Conversely, a school with limited resources can still have high student achievement if the teachers are effective and the curriculum is well-designed.
Therefore, the most important indicator of quality of education in a school is student achievement level.