This document lists words that feature the ten most complex clusters in English, including /str-/, /skr-/, /spr-/, /skw-/, /spl-/, /sl-/, /fl-/, /fr-/, /shr-/ and /thr-/. Research has demonstrated that teaching complex clusters leads to system-wide changes in a child's sound repertoire and increased overall intelligibility. In particular, three-element clusters (e.g., /str-/) imply the presence of two-element clusters and singleton sounds. Complex two-element clusters (e.g., /fl-/) imply the presence of other two-element clusters and also lead to gains in intelligibility. Please also refer to the information on the Sonority Sequencing Principle for Clusters document.