Genome-wide CRISPR-Cas9 screens have untangled regulatory networks driving diverse biological processes. Their success relies on interrogating specific molecular phenotypes and distinguishing key regulators from background effects. Here, we realize these goals by optimizing CRISPR interference with barcoded expression reporter sequencing (CiBER-seq) to dramatically improve the sensitivity and scope of genome-wide screens. We systematically address technical factors that distort phenotypic measurements by normalizing expression reporters against closely matched promoters. We use our improved CiBER-seq to accurately capture known components of well-studied RNA and protein quality control pathways. These results demonstrate the precision and versatility of CiBER-seq for dissecting cellular regulation.