quintile of City schools with greatest student need. Classifying teachers who either were uncertified or had less than three years' experience as novice teachers, Dr. Lankford testified that nearly a quarter of all City teachers, and nearly a third of the teachers in the neediest quintile of City schools, were novices. And he reviewed the colossal failure rates of City teachers on the State's certification content- specialty tests, which rise above 40 percent in mathematics, even for math teachers currently teaching in New York City public schools. As the trial court's decision shows, the record contains many more facts proving a serious shortfall in teacher quality in New York City schools, proving that this shortfall results from those schools' lack of competitiveness in bidding for and retaining personnel, and proving that better teachers produce better student performance ( see 187 Misc 2d at 25-36). On this last point the testimony of Dr. Ronald Ferguson is particularly revealing. Using data from Texas -- where all teachers are tested -- Dr. Ferguson demonstrated that in districts where teachers perform badly on teacher certification tests, student performance declines as student grade level rises -- and, conversely, that where teachers test well, student performance at higher grade levels surpasses student performance at lower grade levels; thus, the longer students are exposed to good or bad teachers, the better or worse they perform. Based on evidence offered by Dr. Lankford, Dr. Ferguson projected that the same correlation would apply in New York. Defendants' expert, Dr. Eric Hanushek, challenged Dr. Ferguson's conclusions, but the trial court rejected this challenge and the Appellate Division -- though it referred to Dr. Ferguson's testimony -- did not rest any of its own contrary findings on Dr. Hanushek's testimony. In sum, we conclude that the Appellate Division erred in relying solely on principal evaluations, and we agree with the trial court's holdings that teacher certification, test performance, experience and other factors measure quality of teaching; that quality of teaching correlates with student performance; and that New York City schools provide deficient teaching because of their inability to attract and retain qualified teachers. School Facilities and Classrooms. As we noted in CFE, children are entitled to "classrooms which provide enough light, space, heat, and air to permit children to learn" (86 2 at 317). The trial court divided this further -- considering first the physical plant of New York City schools, and then the specific problem of overcrowding and class size -- and concluded that New York City schools are deficient. The court conceded, however, that the harmful effect of