CEDAR RAPIDS — While a number of Cedar Rapids schools have improved, the latest round of Iowa School Report Card ratings released Wednesday keeps most of the district’s schools in the lower half of its six-tier system.The school accountability system, run by the Iowa Department of Education, relies primarily on statewide assessment test scores and classifies public schools — from the highest to lowest categories — as exceptional, high-performing, commendable, acceptable, needs improvement or priority.Compared with last year, seven schools in the Cedar Rapids district improved, while ratings at six schools fell.Since the state made the first Iowa School Report Card public in 2015, no school in the Cedar Rapids district, the second-largest in the state, has been placed in either of its two highest tiers.